Fix constructor bug and make Wendland as a package class

 - Correct the mistake that Wendland(4) get a C6-continuous instance
Change WeightFunction.values more flexible

 - The parameter "dists" and "infl_rads" could be just iterable objects.
 - "dists" about nosetests seems well
 - "infl_rads" test haven't been build yet.
Build tests for dynamic influence radius for MLS, and pass it

 - also infers that the WeightFunction passed the tests
 - not that this tests is still very black-box
Refactor some functions' names in mls tests
refactor Wendland instance name and format weight_funcs.py

 - without refactor, Wendland won't run propoperly(Bug fix)
 - refactor self.diff_order to self._diff_order
Make and test CSRbf (Compactly supported radial bases)

 - make a simple test
   - this test also covers Wendland(4)
 - some complex test and written and commented for rbf convergence is not like mls
refactor weight_funcs, and wrap triple_spline with TripleSpline

 - rename weight_funcs to radial_funcs
 - rename WeightFunction to RadialFunction
 - create TripleSpline
 - make RadialFunction constructor more restrict
Refactor bases_func to nomomial_basis

 - rename Monomial_bases to Monomial_basis
 - rename monomial_bases to monomial_basis
 - rename mls's *bases to *basis
Format model.py code style
Add Node and Segment2D in model.py
Make Polygon2D be available for multi-chain polygons and also make Polygon2D be iterable

 - modify __init__ raycrossing distance_func accordingly
 - move distance_to_segment to Segment2D.distance_to
 - demo in modify.py seems good
Convert model.py to a package

 - make package model
 - split model.py into nose.py segment.py polygon.py
 - make Node, Segment2D and Polygon2D be package class in model/__init__.py
 - rename Polygon2DIterator to _Polygon2DIterator
 - demo of polygon.py seems good
Change the sample_vertes_xys() and relative demo in polygon.py

 - the new sample add a hole in demo
Improve _Polygon2DIterator by adapting the iterable character of chains_heads