update inline docu
fix degenerate multipolygon detection

as well as the sanitation of incomplete mps (empty clusters or rings)
remove dead code
update degenerate polygon test

the expected behaviour here is that osmtogeojson does not return a
degenerate (multi)polygon.
it could in principle return just the way that is now sort of unused
but just as with an (untagged) node of a one-node-way we're going to
assume that those outlines aren't interesting enough.
Merge branch 'gh-pages' of github.com:tyrasd/osmtogeojson into gh-pages