fixed bug in basis evaluation
Implemented universal function for bspline basis and derivative. Fixed basis span.
Erased comments
Fixed case for non open knot spans.
Merge pull request #30 from mtezzele/fix_bspline

Now basis evaluation can be done also on non-open knot vectors.
A preliminary version.
A first attempt to write the class using numpy
Some documentatios has been added
print norm of L N B
collecting all the stuff in one class
all the stuff has been moved in arc_length_curve.py
a test for a test of arc_lenght_curve.py
comments
Some asserts have been added in order to check inputs
merging