Document web module

[Luni-4]

This PR fixes #383.

Unfortunately doc tests on binary cannot still be executed because of rust-lang/rust#50784 (comment), but we can create them the same waiting for the feature to be implemented

Otherwise we can transform this module in a lib, with a binary associated, in this way we can document all APIs and at the same time having an executable

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (726de3d) 74.18% compared to head (4260831) 74.19%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1041   +/-   ##
=======================================
  Coverage   74.18%   74.19%           
=======================================
  Files          64       65    +1     
  Lines       15915    15916    +1     
=======================================
+ Hits        11807    11809    +2     
+ Misses       4108     4107    -1     

Impacted Files	Coverage Δ
...ode-analysis-web/src/bin/rust-code-analysis-web.rs	8.33% <ø> (ø)
rust-code-analysis-web/src/web/comment.rs	100.00% <ø> (ø)
rust-code-analysis-web/src/web/function.rs	100.00% <ø> (ø)
rust-code-analysis-web/src/web/metrics.rs	94.44% <ø> (ø)
rust-code-analysis-web/src/web/server.rs	69.03% <ø> (ø)
rust-code-analysis-web/src/lib.rs	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[Luni-4]

I finished documenting the web module, converted it in a library in order to add more tests and doc-tests, and also improved the server test