DOC: reformat docstrings, code to standards

Reformat docstrings and expand docstrings for numpy docstring standard.

Change code spacing to PEP8 (remove blank lines, mainly)
RF: refactor imports to standard order

Put imports in standard order; use relative imports where possible.
RF: remove binary_threshold

binary threshold is a one-liner in numpy; use that line instead.
DOC: extend applymask docstring

Make applymask docstring more explicit
DOC: fixes to median_otsu docstring

Fixes suggested by Stefan VdW
Merge pull request #237 from matthew-brett/refactor-median-otsu

WIP: cleanup docs / small refactor for median otsu
NF: added streamtube visualization mathod in fvtk
playing with colors and lighting properties
RF: started cleaning up the fvtk module. Removed unused functions and put all colors to be used for example with fvtk.colors.red rather than fvtk.red
DOC: on point glyphs
RF: renamed pretty_lines to streamtubes
DOC updated examples to use streamtubes