rustreleasechannel: a data structure for Rust release channel metadata

Repository: https://gitlab.com/Screwtapello/rust_release_channel/

Documentation: https://docs.rs/rust_release_channel

TODO

• Store hashes as bytes rather than hex-encoded bytes?
  • might make it easier to compare with the results of other hash functions
• Teach .validate() to check that in the rename map, the new name is different from the old name.