Change character constants to enums

[bryanforbes]

No description provided.

[coveralls]

Coverage remained the same at 100.0% when pulling b0e87c5 on bryanforbes:use-enum into 568bada on jtauber:master.

[jtauber]

sorry, I merged the other PR first. Can you update this to resolve the conflict? Also can you add yourself to the AUTHORS file?

[jtauber]

would also be good to add some comparison tests which, beside getting coverage % back up, would make sure the comparison you're doing is correct.

I presume the idea is that the Accentuation order based on mora location. That's worth documenting and testing.

[bryanforbes]

I added the comparison methods because sorted() requires __lt__ and adding only that method seemed incomplete. I'll add some tests in extra.rst to exercise them.