Switch to Language enum

[spenserblack]

This PR changes the implementation from interpreting language definitions as compile-time to runtime.
This drastically changes the API, both by simplifying it using implementation that can only be used
with compile-time definitions, and also by removing APIs that are impossible without runtime
language definitions.

To do

• Write enum
• Add methods for enum
  • By extension
  • By filename
  • By shebang
  • By glob
  • Filter by heuristics
  • Pick by priority
• Use enum instead of Language struct
• Implement serialization so that Language struct can be used in JSON output (private LanguageAttrs struct?)
• Replace Analyzers::pick with Language::pick
• Remove serde_json and serde_yaml dependencies on main crate (and anything else that runtime parsing depends on)

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (23de7fd) 87.88% compared to head (69e3e56) 75.05%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
gengo/src/lib.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #298       +/-   ##
===========================================
- Coverage   87.88%   75.05%   -12.83%     
===========================================
  Files          18       17        -1     
  Lines         619      425      -194     
===========================================
- Hits          544      319      -225     
- Misses         75      106       +31     

Flag	Coverage Δ
--no-default-features	73.81% <96.66%> (-13.90%)	⬇️
--no-default-features --features color	74.58% <97.43%> (-10.23%)	⬇️
macOS-latest	66.26% <97.43%> (-21.17%)	⬇️
ubuntu-latest	72.44% <97.22%> (-12.07%)	⬇️
windows-latest	56.90% <79.48%> (-8.08%)	⬇️

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