Fix LED pin enum

* Fix LED pin enum, first one should start at 1
* Fix LED initialization typo
Initial support for Teensy 3.1
Use constructor to create small int (avoid exposing mp_obj_t internals to VM).
Typo fix in comment.
Added dict iterator.
Added dict.clear.
Added 0 to the list of primes. Funky primes, these.
make dict_len use the map's used count
Added dict.copy
Added dict.get.
implemented dict.pop
Added dict.popitem
Added dict.setdefault
py: Fix up number operations and coercion.
stm: Re-fix LED defines.
added a first pass of dict.update
forgot to add test for dict.update
Merge remote-tracking branch 'upstream/master' into dict_feats
Merge remote-tracking branch 'upstream/master' into dict_feats
Moved dict methods out to a mp_method_t.
Merge pull request #108 from chipaca/dict_feats

Dictionary features that don't involve views or classmethods. First part of issue #99.