[Bf-python] BMesh python api proposal.

[joe]

Thanks a lot for doing this, Campbell.

For bmop access, it might be necassary to extend the BMOpDefine struct
a bit.  I propose we call the module either bm or bmesh, I've never
liked the bme abbreviation.   For topological functions, we might want
to try them embedded in the geometry objects (e.g. "vert.dissolve()")
although I don't know if that will work, and some functions may need
to be in the module space.

Submodules might be a good idea, though I'd suggest avoiding the word
"kernel", which may imply more mathematical underpinning than actually
exists.  I'm not sure if loop_next and loop_prev need to be in the
loop wrapper (isn't that what iterators are for?) and having an
iterator for radial loops would be nice too.  You should be able to
write some sort of wrapper around the BMIter API.