Fix errors in relabel_from_one docs; PEP8
Update snippets in notes to use double backticks
Merge pull request #726 from jni/fix-relabel-doc

Fix errors in relabel_from_one docs; PEP8
ENH Faster perimeter computation

Measured a 30% speedup on a 640x640 image. Fundamentally, this makes
fewer passes over the image; so it should never be worse that the
previous implementation.
RFCT Simpler code for initializing array

Also, replaced skimage.measures.histogram by np.bincount.

Both changes were suggested in the pull request discussion by Juan
Nunez-Iglesias (jni):

https://github.com/scikit-image/scikit-image/pull/746
Merge pull request #746 from luispedro/master

ENH Faster perimeter computation
Some improvements for perimeter
Add support for unsigned integer label images
Raise error for non 2-D images
Fix dtype bug in perimeter
Merge pull request #748 from ahojnnes/regionprops-dtype

 - Fix for regionprops dtype error (#747) and additional tests.
 - Some docstring improvements.
Remove call to deprecated is_gray function
Misc doc string fixes
Only clip for ndimage.map_coordinates case
Add note about internal usage of transformation matrix
Add support for matrix as inverse_map
Improve example of warp function to show all available options
Fix deprecated function name in example
Merge pull request #750 from ahojnnes/misc

Misc cleanups.
PEP8: comparison