Use setuptools. Don't install demos.

setuptools provides the "setup.py develop" feature
No need to install demos, just provide them in repo
Ignore backup files *~
Various files are no longer executable.
Cleaned up plotting in Crv.py
Updated some information in __init__.py
Use class NURBSError(Exception)
Crv.Crv inherits from object (new-style class), added simple doctests

Changed other classes to use calls to super()
Added some comments
Merge pull request #1 from KneeShard/crv_minor_cleanup

Updates to curve manipulation scripts
Thanks for these additions, excellent work!