Improve documentation

[marfox]

Missing features in the current Mediawiki page, as compared to what I consider a gold standard, i.e., http://docs.python-requests.org/en/latest/api/
ordered by priority:

1. usage commands (only needed for prominent functions of the NLP pipeline, e.g., https://www.mediawiki.org/wiki/StrepHit#strephit.commons.pos_tag_module);
2. arguments type, cf. https://www.mediawiki.org/wiki/StrepHit#strephit.annotation.post_job_module
3. internal classes anchors;
4. source code links;
5. return type anchors/links.

[marfox]

Points 3,4 and 5 above are to be implemented yet.

[marfox]

More comments. These are the minimal requirements to make the documentation more usable:

1. do not generate non-browsable lists, e.g., https://www.mediawiki.org/wiki/StrepHit#Subpackages
2. avoid empty sections, e.g., https://www.mediawiki.org/wiki/StrepHit#Module_contents