Document btparse support

README.md

@@ -35,12 +35,72 @@ BacktracePrinter::new().message("Custom message!").install(default_output_stream
 ```
 
 ### Features
+
 - Colorize backtraces to be easier on the eyes
 - Show source snippets if source files are found on disk
 - Print frames of application code vs dependencies in different color
 - Hide all the frames after the panic was already initiated
 - Hide language runtime initialization frames
 
+### Reducing transitive dependencies
+
+It is possible to use the alternative [`btparse`] backtrace capturing backend
+instead of the default route that links [`backtrace`]:
+
+```
+[dependencies]
+color-backtrace = {
+  version = "0.6",
+  default-features = false,
+  features = ["use-btparse-crate"],
+}
+```
+
+This reduces the number of transitive dependencies from around 12 to just 2. So
+why isn't this the default, you may ask? There's a stability tradeoff here:
+`btparse` relies on the **undocumented and unstable** `std::fmt::Debug`
+implementation of `std::backtrace::Backtrace` to remain unchanged. As of writing,
+this has been untouched for 4+ years, but there's no *guarantee* that it will
+always work.
+
+[`btparse`]: https://github.com/yaahc/btparse
+[`backtrace`]: https://github.com/rust-lang/backtrace-rs
+
+<details>
+<summary>Dependency tree with `use-backtrace-crate` (default)</summary>
+
+```
+$ cargo tree
+color-backtrace v0.6.1 (/Users/ath/Development/color-backtrace)
+├── backtrace v0.3.73
+│   ├── addr2line v0.22.0
+│   │   └── gimli v0.29.0
+│   ├── cfg-if v1.0.0
+│   ├── libc v0.2.155
+│   ├── miniz_oxide v0.7.4
+│   │   └── adler v1.0.2
+│   ├── object v0.36.1
+│   │   └── memchr v2.7.4
+│   └── rustc-demangle v0.1.24
+│   [build-dependencies]
+│   └── cc v1.1.1
+└── termcolor v1.4.1
+```
+
+</details>
+
+<details>
+<summary>Dependency tree with `use-btparse-crate` (default)</summary>
+
+```
+$ cargo tree --no-default-features --features=use-btparse-crate
+color-backtrace v0.6.1 (/Users/ath/Development/color-backtrace)
+├── btparse v0.2.0 (https://github.com/yaahc/btparse.git?rev=54f9ddb8c7c8f8e034226fdcacab93cd76e1453b#54f9ddb8)
+└── termcolor v1.4.1
+```
+
+</details>
+
 ### Usage in tests
 
 Unfortunately, defining custom init functions run before tests are started is