Renamed `access::Access` to `ArchetypeAccess`, made it private. No particular reason.
Removed `ThreadLocalExecution`, `System::thread_local_execution()` - this information is now encoded in `::archetype_component_access()`, `::resource_access()`, and new `::is_thread_local()`.
Extended `TypeAccess` with support for "reads/writes everything" to facilitate the above.
Renamed `ThreadLocalSystemFn` and the module `into_thread_local` to `ExclusiveSystemFn` and `into_exclusive` respectively, to differentiate systems with this access pattern from actually thread-local systems.
Implemented `IntoSystem` for `FnMut(&mut World)` and `FnMut(&mut Resources)`, both result in `ExclusiveSystemFn`. Just because. Probably in vain.
Rewrote `SerialSystemStageExecutor` to account for `ThreadLocalExecution` removal.
Implemented `ThreadLocal` system parameter.
Implemented mk1 label and dependencies methods on `SystemSet` and `SystemStage`.
Added `ShouldRun::NoAndLoop`.

Renamed `System::update()` to `System::update_access()`, for clarity.
Plumbed labels and dependencies into the stage executor, via `SystemStage::labels` (a stage-global map of label to system index), `SystemSet::system_label()`, and `SystemSet::system_dependencies()`.
Rewrote `SerialSystemStageExecutor` to support exclusive systems at start of stage as well; unfinished.

Began implementation; doesn't do anything yet because the pathway from data it gets to data it wants is not implemented.
Changed system sets to store systems in `NonNull` rather than `Box`. Requires auditing and a sanity check.

Minor cleanup.
Partially implemented run criteria handling.

Minor refactor.
Fixed a future bug in not yet implemented `can_start_now()`.
Accounted for run criteria for parallel systems: if a system shouldn't run in this iteration, its task is not spawned and it's never queued to run.

Added `CondensedTypeAccess` and related machinery.
Moved the dependency resolution burden from executor to the stage; verification is not yet implemented.
Systems with no dependencies are immediately queued to run at the start of each iteration.
Implemented rebuilding scheduling data and updating access information.
Implemented `can_start_now()`.

Running tests violates access, right now.

# Conflicts:
#	crates/bevy_app/src/app.rs
#	crates/bevy_app/src/app_builder.rs
#	crates/bevy_asset/src/lib.rs
#	crates/bevy_core/src/time/fixed_timestep.rs
#	crates/bevy_ecs/Cargo.toml
#	crates/bevy_ecs/src/lib.rs
#	crates/bevy_ecs/src/schedule/mod.rs
#	crates/bevy_ecs/src/schedule/stage.rs
#	crates/bevy_ecs/src/schedule/stage_executor.rs
#	crates/bevy_ecs/src/schedule/state.rs
#	crates/bevy_ecs/src/system/into_system.rs
#	crates/bevy_ecs/src/system/into_thread_local.rs
#	crates/bevy_ecs/src/system/system.rs
#	crates/bevy_ecs/src/system/system_chaining.rs
#	crates/bevy_ecs/src/system/system_param.rs
#	crates/bevy_input/src/lib.rs
#	crates/bevy_render/src/lib.rs
#	crates/bevy_render/src/render_graph/system.rs
#	crates/bevy_scene/src/lib.rs
#	crates/bevy_transform/src/hierarchy/hierarchy_maintenance_system.rs
#	crates/bevy_transform/src/transform_propagate_system.rs
#	crates/bevy_ui/src/lib.rs
#	crates/bevy_ui/src/update.rs
#	crates/bevy_winit/src/lib.rs
#	examples/2d/texture_atlas.rs
#	examples/ecs/ecs_guide.rs
#	examples/ecs/fixed_timestep.rs
#	examples/ecs/state.rs

It was one space, CI, come on now.

# Conflicts:
#	crates/bevy_ecs/Cargo.toml
#	crates/bevy_ecs/src/schedule/mod.rs
#	crates/bevy_ecs/src/schedule/stage.rs
#	crates/bevy_ecs/src/schedule/stage_executor.rs

Implemented (probably incomplete) `SystemDescriptor`, its coercion machinery, and its usage in `SystemStage` (parallel dependency tree is still not validated). Plumbed more data between stage and executor to make use of the latter.
Removed most of system insertion methods on `SystemStage` and `SystemSet`, replaced remaining with those taking `Into<SystemDescriptor>` (except `App`).
Simplified cache invalidation trigger in `SystemSet`; need to verify if any of it, along with its usage, could/should be moved to initialization instead.

Removed the check that forbade parallel systems to be used in the exclusive system queues, altered exclusive system execution to also run the parallel part.
Changed language in `SystemStage` and the executors to reflect the above: "exclusive" systems are now "sequential".
Moved `ParallelSystemStageExecutor` to its own file.
Refactored the two executors to share more code; moved parallel system preparation in parallel executor to its own function, `::prepare_parallel_systems()`.
Minor renames.
Removed `SerialSystemStageExecutor::last_archetypes_generation`: this is used only to update access, and access is used only to parallelize things, so a strictly serial executor has no need of it.

Should've done a `cargo clean` long ago.

Introduced `_exclusive` system insertion methods throughout the API (except states).
Rearranged system insertion methods in `AppBuilder`; no particular reason.
Renamed `System::run_exclusive()` to `apply_buffers()` to better reflect its function.
Blindly made all exclusive systems in the engine be inserted with the appropriate methods; haven't done anything wrt validity of the resulting execution order.

…gly.

# Conflicts:
#	crates/bevy_ecs/Cargo.toml

…ting where applicable; more documentation.

… `SystemSet` and `ShouldRun` to the prelude; renamed `SystemStage::serial()` and `SerialSystemStageExecutor` to `::single_threaded()` and `SingleThreadedSystemStageExecutor` respectively; minor refactors.

… now responsible solely for parallel systems execution; renamed things to make sense with that change; moved `SystemSet` to its own module.

…chained systems; minor refactors; more tests.

…" bitset to `SystemStage`.

…ype-agnostic component access for parallelizable systems.

… time; more tests; minor refactors.

…worked exclusive systems to use separate and unambiguous `IntoExclusiveSystem` trait.

…removal of `Send + Sync` bound from `Stage`.

…; more tests.

# Conflicts:
#	crates/bevy_app/src/app_builder.rs
#	crates/bevy_ecs/src/schedule/stage.rs
#	crates/bevy_gilrs/src/lib.rs
#	crates/bevy_winit/src/lib.rs