use setuptools:

* declare requirements
* use 2to3 feature of setuptools
* some minor doc fixes
fixing travis
Clearer comment.
Merge branch 'setuptools' of github.com:mindw/uncertainties into mindw-setuptools
More robust PDF documentation generation in Makefile. Fixed EPUB information message.
Simpler and more explicit abspath call.
setup.py now uses setuptools if available, or falls back to distutils.
Moved back use_2to3 to the setuptools-only configuration (got a warning with distutils).
Added missing minimum version for the setup.py install --user option.
Merge branch 'master' into mindw-setuptools
Fixed Python case.
Removed useless ReST link.
Specific git ignores removed (https://github.com/mindw/uncertainties/commit/0eee730c10b32378e7a63f881765a4891022e1ac).
Regression fixed: "nosetests-2.6 -sv --with-coverage --cover-package=uncertainties --cover-tests --exclude=unumpy uncertainties/" failed on my machine (OS X with MacPorts).
Merge branch 'mindw-setuptools'. Important modifications compared to the original commit c63824ec9ae9fd5b3a5117b24936af9507875e65.