👀 hot shader reloading

[DJMcNab]

Add a (feature gated) implementation of hot shader reloading to SpirvBuilder

This attempts to handle initial compilation gracefully by watching the shader crate root recursively until we have more detailed dependency information

Unfortunately, notify uses a non-standard license (CC0) so we fail the cargo deny check. I will defer adding a commit which changes deny.toml to allow this to pass to the suitable Embarker (@XAMPPRocky ?)

It appears that if there was sufficient demand for it, notify would be willing to update their license ( notify-rs/notify#243 (comment))

In theory, the CC0 license they are under is probably already MIT/Apache compatible, so notify could avoid getting new permissions from the contributors, but it would still be wise to notify (ha) them.

(See e.g. this stackoverflow post (this is google's webcache since stackoverflow is down at the time of posting))

I'm also planning to integrate this into the example runner, but want to get the ball rolling on the license issues

[DJMcNab]

I have produced a video showing how this works in the wgpu example runner:

2021-06-08.21-17-24.mp4

[khyperia]

LGTM, just the two things!

[khyperia]

Unfortunately, notify uses a non-standard license (CC0) so we fail the cargo deny check. I will defer adding a commit which changes deny.toml to allow this to pass to the suitable Embarker

Pushed the exception!