lots of refactoring, lots of unit tests

[bocajnotnef]

Refactored the AlphaSequence class to contain all the validation then cleaned up the validation handler so it can swap out what kind of sequence we're checking as well.

doing all that then required hella testing to increase coverage, so now we've got a ton of mocking going on and lots more unit tests

Some things to consider:

• Should the validate handler return something other than none, if only so our tests can get more meaningful output?
• Should we rename the validate handler to something like validate_handler_func?

This will address #8

[bocajnotnef]

Oh, and I nuked some code that isn't used anymore after @marcvberg's refactor