interval default value; use const()

[dhalbert]

Hi @dastels, didn't have a chance to review this before today. Just a couple of comments;

Adafruit_CircuitPython_Debouncer/adafruit_debouncer.py

Line 71 in c7a4a8e

if interval is None:

1. Why check for interval is None in the constructor if it already has a default value? I think self._interval = interval would be sufficient.

2. Do

from micropython import const
...
_DEBOUNCED_STATE = const(0x01)
_UNSTABLE_STATE = const(0x02)
_CHANGED_STATE = const(0x04)

This will, at compile time, substitute the integer values for the names. This speeds up the code and makes it smaller. The underscored names will actually disappear from the compiled code because they aren't exeternally available. See
http://docs.micropython.org/en/latest/reference/speed_python.html#the-const-declaration
and
http://docs.micropython.org/en/latest/library/micropython.html?highlight=const#micropython.const

[dhalbert]

Fixed by #6.