refactor FlxTypeText to better manage it's current status

[ninjamuffin99]

Bit of some cleanup R&D for FlxTypeText as I've been poking around in it.

I was getting tiny annoyed at 4 different variables to manage paused, typing, erasing, waiting, and the different combination of those, so I organized the logic for that a bit into this

internally something like

if(_typing && !_waiting && !_erasing)

becomes

if(_status == TYPING)

also added a few extra public functions
pause(), resume() and stop()
each function is documented

I am trying to get good reps and practice in for lil design / code organization like this, so if it rough around the edges let me know if theres something that should be more consistent with flixel or anything like that!