Parsers with optional semantics

We need to have the parse_*_int methods not crash when they aren't specified. I'd have loved to use partials, but stupid 2.4 doesn't support them. So now we have a few parse_optional_* methods.

I took this opportunity to pull the generic parsers into okaara itself. The bulk of this change is to remove the parser methods from Pulp or to add in aliases from the old Pulp names to the new names in Okaara because I'm compulsive and changed a few.

This doesn't fix the actual bug that revealed the issue about optional parameters, but I'll do that in a different PR.

For reference, here's the commit in Okaara: https://github.com/jdob/okaara/commit/7fc50439939fe9e0b60dab8a8e51720f99d47830