* Add sources and resources for each version of Rust
* install bootstrapping compiler into stage
* Add libgit2
* Install bootstrapping compiler correctly
* implement full rust bootstrap
* Remove support for Rust pre-1.14
Also add lots of comments
* Support only Rust 1.17 and newer
* Remove < 1.23 versions of Rust
* Change the layout of rust_releases for maintainability
* Remove LLVM variant
* Address flake8 issues
* Make libgit2 curl variant default False, conflict 0.28 and newer
* Remove binutils dependency
* Add ARM64 while we're at it
* flake8
* use the 'python' routine rather than relying on the correct python to be picked up
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