make sets iterable
Implemented set.add
Implemented set.clear
Implemented set.copy
Implemented set.discard
Implemented set.difference and set.difference_update
Implemented set.intersection and set.intersection_update
Implemented set.isdisjoint
Added a hacky implementation for %g
Implemented set.remove
Implemented set.update
Implement a basic str.find; fixes #67
Implemented set binary ops.
oops, nasty off-by-one in set_copy
stm: Re-instate C debugging USART port (disabled by default).

See pyb_usart_global_debug variable.

Also did some work on USB OTG, but nothing working yet.
Merge pull request #157 from dhylands/printf-float

Added a hacky implementation for %g
Merge pull request #159 from chipaca/set_feats

Set features. As per #143.
Merge pull request #160 from pfalcon/elaborate-int

Elaborate small-int/long-int
Merge pull request #162 from chipaca/str_find

Implement a basic str.find; fixes #67
Add MP_OBJ_TYPE(o) accessor.

Should not be overused, but when needed, it's needed.