Adds auxcov Code Coverage library

[Cyberboss]

• Splits the debug_server crate into a new instruction_hooking crate.
• Adds auxcov crate which uses instruction_hooking to provide line by line code coverage. (GPL)
• Adds setting for rust-anaylzer which properly sets the target to i

Working concept can be viewed here: https://app.codecov.io/gh/tgstation/tgstation

[Cyberboss]

Please see #66 for the build fixes

[willox]

Pretty much looks fine, this probably won't call for a new debug_server release.