[#39] Tests on autodoc

Description

Problem: it's too easy to break generated documentation entirely and it's often hard to notice that.

Solution: test various simple predicates on documentation like "all entrypoints have description".

AFAIU this covers mostly all breakages which we had at this moment, except the one when part of doc got lost after the corresponding code being moved to storage. The latter I want to resolve separately (see #49) because it's not yet entirely clear which way to ensure this will be the best one, need to collect more data about accidents.

Recommended review order of the main commit:

• Michelson.Doc.Test
• Everything else.

Related issue(s)

Resolves #39 (closed)

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• Tests (see short guidelines)

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    • Haddock
    • docs/
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