Add `**open_options` to FileWatcher

[foklepoint]

Currently, a FileWatcher can't be forced to open() a file with a specific encoding type. This is necessary when you don't want to fallback to the platform encoding and instead force a file to be opened as a specific encoding type (i.e: utf-8)

A proposed solution is to add **open_options kwargs to FileWatcher.__init__

This would also allow the FileWatcher to modify the open operation in the following ways:

mode='r'
buffering=-1
encoding=None
errors=None
newline=None
closefd=True
opener=None

[pacejackson]

Note, this is really only applicable to Python 3. Python 3 has several options while Python 2 does not

[pacejackson]

Addressed in #250