add user guide parallelization
setup
Added support for different illuminants.
Added new tests. The support for a wider range of illuminants is now tested.
Added tests for the new functionality.
Comments of the PR
Added gitwash as an option on the makefile.
Updated the gitwash build.
Undone change in skimage/__init__.py.
The format strings were updated to include numbers.
Stephan's comments
Corrected code to conform to Python coding conventions (PEP 8).

Added test code for handling exceptions.

Corrected test code to use the full path to the test data.
Fix indexing bug in freeimage plugin
Fix Big Endian check
Merge pull request #1114 from pelson/gitwash

Update gitwash
simplify notations
Merge pull request #1043 from sciunto/joblib

DOC: Add user guide parallelization
Merge pull request #1135 from stefanv/freeimage_big_endian

Fix indexing bug in freeimage plugin (closes #1111)
Added Stephan comments.

Syntax is now checked using `flake8`.
BUG: add signed flag to chars

Sign of char is undefined and there are numerous places where its sign
is important. Fixes tests with -funsigned-char.
Closes gh-1110