Code improvement, part 1: modules documentation

[ProgramCrafter]

In particular, several doc-links which pointed nowhere were fixed. This code should also pass Clippy's and rustfmt's judgement.

[codecov]

Codecov Report

Attention: Patch coverage is 73.68421% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 61.68%. Comparing base (cc7e2ba) to head (e8d498a).

Files	Patch %	Lines
webrtc/src/peer_connection/sdp/sdp_test.rs	61.11%	0 Missing and 7 partials ⚠️
webrtc/src/ice_transport/ice_candidate.rs	76.92%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #549      +/-   ##
==========================================
- Coverage   61.70%   61.68%   -0.03%     
==========================================
  Files         529      529              
  Lines       48870    48828      -42     
  Branches    12273    12250      -23     
==========================================
- Hits        30157    30119      -38     
+ Misses       9580     9548      -32     
- Partials     9133     9161      +28     

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[ProgramCrafter]

Those four lints failing Clippy check are fixed! Or, more precisely, one lint was incorrect so it was locally-allowed.