unix: Add GC support for ARM architecture.
Add basic collections.namedtuple implementation.
Add mp_obj_is_subclass_fast() - intended for fast argument checking.

I.e. as replacement of MP_OBJ_IS_TYPE(), which takes into account subclassing.
namedtuple: Inherit unary/binary ops from tuple base class.
Merge pull request #332 from pfalcon/namedtuple

Implement collections.namedtuple
py: Factor and improve issubclass.
py: Unify syntax error handling in compiler; check defualt arg syntax.

Checks for non-default args following default args, and errors out.
Addresses issue #328.
py: Fix overriding of default arguments.

Addresses issue #327.
unix: Allow to set heap size using "-X heapsize=N" option.
Merge pull request #333 from pfalcon/heapsize-cmdline

unix: Allow to set heap size using "-X heapsize=N" option.
unix: Add to usage print-out telling about -X option.
Fix gc_realloc to expand in place

* Issue #322
Merge pull request #334 from iabdalkader/realloc

Fix gc_realloc to expand in place
py: Small cosmetic changes to gc_realloc.
py: Add comments to new gc_realloc, it has some bugs.
py: Revert to old gc_realloc for now.