Rust rewrite

[sirbrillig]

This PR completely replaces the old node version of this project with a brand-new rust version. The command-line API remains nearly the same, with a few differences:

• The short version of --version is now -V (capitalized) instead of -v.
• The --searcher and --reporter options no longer exist (note that both only had one option).
• The --verbose option no longer exists as there is no subcommand being run.
• It no longer requires node or ripgrep to be installed; searching is done manually (but still very fast).

It should work interchangeably with the vim and vscode extensions.

This also adds Rust support to the tool.