Avoid extensive usage of nodoc

[BuonOmo]

While adding new features, I could not retrieve them using ri or irb> polygon.make_valid!<tab><tab>. This was due to the fact that :nodoc: prevents documentation from handling correctly all of *Impl, and thus, could not redirect to documented methods correctly.

IMHO, we should consider:

1. Removing most :nodoc:, checking if there is a real usage somewhere first,
2. See the size augmentation of doc related to the repo (using rdoc),
3. If (2.) concludes in too much documentation, or if we end up generating doc for tests, add options to make sure documentation is parsed correctly both by:

• yard (for rubydoc.info)
• rdoc (for ri tools, irb> my_feature.some_method<tab><tab> is a good test)

4. add related tests if feasible.