One Dimensional AST Implementation

Implemented one dimensional madness that uses AST to evaluate expression on functions. It does a single tree traversal for the entire expression. Intermediate coefficients are consumed as soon as they are created, hence, intermediate trees are not created. Please refer to onedAST.py for details. 

This approach to evaluating expression of functions in MADNESS will reduce the number of global synchronizations and improve locality by avoiding intermediate. Such implementation should improve scalability of MADNESS.