Add cargo xtask msrv (#3189)
* added cargo xtask msrv X.Y placeholder function
* add placeholder function cargo xtask msrv (X.Y)
* implement CLI arg vec, graceful errors, formatting
* impl. xtask msrv insert,upsert,graceful failures
* misc fixes - still need to update write method
* interim commit before removing comments
* updated per @djmitche suggestions. 2 fixes todo
* impl unwrap error checks, file truncating, etc
* removed test paths
* updated toml with specific regex version
* updated cargo toml and lock for regex version
* updated cargo toml and lock for regex version
* fixed clippy complaints
* impl replace file content, not comments
* accept djmitche suggestion to change comment documentation
Co-authored-by: Dustin J. Mitchell <dustin@v.igoro.us>
* refactored, need to fix Cow return
* removed debug prints, unncessary if, etc.
* fix non-idiomatic rust, arg.len error handling
* add #MSRV to config files and test
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Co-authored-by: iwyatt <sayhello+git@isaacwyatt.com>
Co-authored-by: Dustin J. Mitchell <dustin@v.igoro.us>
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