[Cython] CyFunction refactoring plan

[Vitja Makarov]

I tried to build simple plan for ongoing cython function refactoring

* Replace assignment synthesis with SingleAssignmentNode, where LHS is
NameNode and RHS is PyCFunctionNode
* Split function body into python wrapper and C function
http://wiki.cython.org/enhancements/generators#Pythonfunctionrefactoring

Then we can implement some features and optimizations:

* Reduce difference between cdef and def functions
* Store runtime evaluated default values inside CyFunction, ticket #674
* Implement no-args super(), ticket #696
* Function call inlining

-- 
vitja.