tomlgen: move to separate package

Author: davidhewitt

CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Removed
 - Remove `test_rust` command. (`python setup.py test` is deprecated.) [#129](https://github.com/PyO3/setuptools-rust/pull/129)
 - Remove `check_rust` command. [#131](https://github.com/PyO3/setuptools-rust/pull/131)
+- Move `tomlgen_rust` command to separate `setuptools-rust-tomlgen` package. [#167](https://github.com/PyO3/setuptools-rust/pull/167)
 
 ### Fixed
 - Use info from sysconfig when cross-compiling. [#139](https://github.com/PyO3/setuptools-rust/pull/139)

README.md

@@ -87,7 +87,3 @@ By default, `develop` will create a debug build, while `install` will create a r
   - `build_rust` - Command builds all rust extensions.
   - `clean` - Standard clean command executes cargo clean for all rust
     extensions.
-  - `tomlgen_rust` - Automatically generate a Cargo.toml manifest based
-    on Python package metadata. See the [example
-    project](https://github.com/PyO3/setuptools-rust/tree/main/examples/tomlgen)
-    on GitHub for more information about this command.