Reorganize wrapper and add search and suggestion

[mgautierfr]

New update of python-libzim.

This PR is pretty big.

• It rewrite a part of the wrapper to have a better organization for our wrapper.
• Add search and suggestion wrapping (in two different submodule)

Better to review commit by commit as the whole change is pretty complex.

Unit tests have been update with last version of the testing zim files.

[mgautierfr]

The failing unit test is fixed in https://github.com/openzim/libzim/pull/625

[rgaudin]

The failing unit test is fixed in openzim/libzim#625

Great! Once this is merged we'll update the nightly we build against

[kelson42]

@rgaudin @mgautierfr What is the review process/status.

[codecov[bot]]

Codecov Report

Merging #119 (1c7c7ce) into update-libzim (38e2114) will increase coverage by 0.71%. The diff coverage is 97.82%.

@@                Coverage Diff                @@
##           update-libzim     #119      +/-   ##
=================================================
+ Coverage          97.11%   97.82%   +0.71%     
=================================================
  Files                  3        1       -2     
  Lines                312      414     +102     
=================================================
+ Hits                 303      405     +102     
  Misses                 9        9              

Impacted Files	Coverage Δ
libzim/libzim.pyx	97.82% <97.82%> (ø)

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[rgaudin]

@mgautierfr, tests are now passing

[rgaudin]

@mgautierfr I also squeezed-in a tiny commit to set the charset on add_metadata's default mimetype. We can add that separately but since it's harmless…