ENH: Represent 3D Frames as scrollablestacks using JS.
ENH: Add scrollable_stack as a top-level function.
DOC: Add docstrings.
REF: Rename export.py -> display.py (not a public API change)
Remove _repr_png_; improve normalization; tweak default size.
Use a random uuid for the DOM id.
Add jijna2 to test env.
FIX: Make base64 encoding py3-compatible.
Merge pull request #116 from danielballan/scroll-interaction

ENH: Represent 3D Frames as scrollablestacks using JS.
FIX: Allow as_grey on RGBA images.
FIX: Ignore (drop) alpha channel if it exists, following skimage.