Initial commit of adapthist modifications.
Tests pass and example works on build.
Added Notes to the docstring.
Pep8 fixes.
Replaced generic ACM license with the Graphics Gems IV license.
Improved support for color images using lab transform.
Passed all tests with full coverage, PEP8 and Pylint performed.
ENH: Allow imread to read URLs
Fix handling of temporary file.

Opening an already-opened file was unsafe. Close the file, then manually delete it.
ENH: Add test and support for reading file URLs
STY: Fix confusing use of context-manager.
Translated clahe C code to python, added to list of contributors.
Removed sys.path hack in test, fixed spelling of import in __init__.py
ENH: Add canvastools subpckages with base class and line tools
BUG: Move callback connection to parent class
STY: Reuse ThickLineTool in LineProfile
BUG: Fix blitting behavior in canvastools
STY: Refactor parts of LineTool to CanvasToolBase
BUG: Clean up imports
Add functions to join and relabel segmentations

The join of two segmentations is the segmentation in which two voxels
are in the same segment if and only if they are in the same segment in
both input segmentations.