changed method __getitem__ to use .mask directly (e.g. df.mask(df > 0) is equivalent semantically to df[df>0])

added inplace keyword to where method (to update the dataframe in place, default is NOT to use inplace, and return a new dataframe)

changed method _boolean_set_ to use where and inplace=True (this allows alignment of the passed values and is slightly less strict than the current method)

all tests pass (as well as an added test in boolean frame indexing)

…al sized frame

thus we now allow: df[df[:-1]<0] = 2 (essentially partial boolean indexing)

all tests continue to pass (added new test to test partial boolean indexing, removed test requiring an equal indexed frame)

removed mask method
made other optional kw parm in where
changed __setitem__ to use where (rather than mask)

added condition testing to where that raised ValueError on an invalid condition (e.g. not an ndarray like object)
added tests for same