Added is_dict_like_node.
Reworked arithmetic/getitem.
Make dict(-like) value evaluation lazy.

Still evaluates all keys. Fixes #14.
Clean up/document PartialPlus tests.
PEP8 spacing.
Test an exception in pylearn2 wrappers.
Test for is_indexable.
Added pyll converter + tests.
Remove dead code, simplify.
Make Literals more lightweight.
Conditional test execution for pyll.
Better ImportError message.
pyll free variable conversion.