Better documentation and better struct/field naming

[lmammino]

This PR introduces a comprehensive programmatic documentation (rustdoc) and renames all the struct fields to be more descriptive (BREAKING CHANGE).

Closes #28
Closes #6

Screenshots

[codecov-commenter]

Codecov Report

Merging #29 (11db80d) into main (a8255c4) will increase coverage by 3.25%.
The diff coverage is 92.65%.

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
+ Coverage   82.16%   85.42%   +3.25%     
==========================================
  Files          10       10              
  Lines        1060     1077      +17     
==========================================
+ Hits          871      920      +49     
+ Misses        189      157      -32     

Impacted Files	Coverage Δ
src/trustlist.rs	58.87% <ø> (ø)
src/valuesets.rs	100.00% <ø> (+8.65%)	⬆️
src/cwt.rs	79.41% <33.33%> (ø)
src/vaccination.rs	57.89% <66.66%> (ø)
src/parse.rs	71.65% <75.00%> (ø)
src/recovery.rs	61.53% <77.77%> (+4.39%)	⬆️
src/dgc.rs	97.52% <97.52%> (ø)
src/dgc_container.rs	78.00% <100.00%> (ø)
src/lib.rs	86.91% <100.00%> (ø)
src/test.rs	95.45% <100.00%> (ø)
... and 5 more

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[lmammino]

Thanks @allevo! Applied your suggestions :)

[lu-zero]

• Neat documentation
• Nicer/Simpler types

I like it a lot.