Update Documentation and display of warning

Updates the documentation and displays in `find_MAP` a warning only when
`disp=True` and discrete variables are specified.
PEP8 Whitespace fixes
Incorrect handling of default fmin

Accidentally overrode fmin when specified
Added discrete `find_MAP` example notebook and .py
Added find_MAP test

Added a test that tests the results of using `find_MAP` on models with discrete
stochastics.
Removed extraneous warnings in example

Removed some extraneous warnings in discrete_find_MAP.ipynb that were due to my
particular environment.