Add missing features documentation

[Stygmates]

The rustdoc isn't up to date with the readme and features documentation is missing. This PR solves this.

[codecov]

Codecov Report

Merging #1260 (589e51f) into 0.4.x (8509c25) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            0.4.x    #1260   +/-   ##
=======================================
  Coverage   91.37%   91.37%           
=======================================
  Files          37       37           
  Lines       16448    16448           
=======================================
  Hits        15030    15030           
  Misses       1418     1418           

Files Changed	Coverage Δ
src/lib.rs	95.58% <ø> (ø)

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[pitdicker]

What I still wanted to do was sync the documentation in lib.rs with the changes to the README in #1111. Do you want to copy those also, instead of only the features (except the part about the license)?

[Stygmates]

What I still wanted to do was sync the documentation in lib.rs with the changes to the README in #1111. Do you want to copy those also, instead of only the features (except the part about the license)?

Done, let me know if you want me to change something else!

[pitdicker]

Thank you!

I am not sure what happened, you have parts of the README with lines from the current docs in between them?

[pitdicker]

Please also squash the commits 😄.

[Stygmates]

All done! Thanks for keeping up with me!

[pitdicker]

Thank you!