const where we can
cleanup
DefaultBackend is now stateless

which is nice
GenApiFile - finals
gen_api: supports an overrides argument

Can now easily generate compatible output w/ the full output generation
gen_api.dart: removed unused method
no points for null LICENSE
avoid multiple iterations of a dynamic iterable
make methods that don't depend on instance state static

Easier to test. Easier to reason about.
Merge pull request #34 from kevmoo/master

More cleanup