FIX: class_exts should return empty set, not empty dict
CLN/PERF: Do not import matplotlib at the module level.
ENH: In notebook, default repr of Frame is PNG.
Merge pull request #62 from danielballan/no-module-mpl

CLN/PERF: Do not import matplotlib at the module level.
Merge pull request #61 from danielballan/exts-set

FIX: class_exts should return empty set, not empty dict
Merge pull request #63 from danielballan/rich-display

ENH: In notebook, default repr of Frame is PNG.
FIX: Maintain aspect ratio in _repr_png.
Merge pull request #64 from danielballan/fix-aspect-ratio

FIX: Maintain aspect ratio in _repr_png.
DOC: Remove OpenCV, add current deps.
ENH: Use skimage.io if available; clean up import chain.
TST: Separately test mpl and pil backeneds of ImageSequence.
Merge pull request #65 from danielballan/release-prep

Release prep
CLN: Remove unused code, legacy from mr.
Merge pull request #66 from danielballan/remove-legacy

CLN: Remove unused code, legacy from mr.
ENH : use better setup tools
Merge pull request #67 from tacaswell/setup_upgarde

ENH : use better setup tools
RLS: Version 0.2
BLD : actually install the extern folder

 - minor PEP8
 - add pims.extern to the package list
FIX: Bug in loading TiffStack into API.
Merge pull request #72 from danielballan/fix-api-bug

FIX: Bug in loading TiffStack into API.