BF: Fix AttributeError on error in MovieStim

Not available logging.Error() was called instead of logging.error().

Found by pylint.
BF: Fix NameError in filters.makeGrating()

Not available Float was used instead of type float.

Found by pylint.
BF: Fix AttributeError and NameError

There were typos in what seems to be an unused class.

Found by pylint.
ENH: Fix typos in docstrings
DOC: Fix duplicate words in documentation
ENH: Fix typo and double quote in docstrings
BF: Fix AttributeError in float_uint16()

float_unit16() tried to access numpy.UnsignedInt16 which is not
available. This was fixed by using numpy.uint16.

Found by pylint.
ENH: Add doctests for two utility functions
Merge pull request #429 from philippwiesemann/fix-errors-found-by-pylint

ENH: Minor bugs in source and typos in docs