Merge pull request #1 from richford/master

Added all py files, an ipython notebook, and updated the readme.
AST files added
One Dimensional AST code added. It can compute expression on functions in a single tree traversal. The operations that can be handled are add, multiply, diff and reconstruction. diff will work only if it is acting on a function, but not on an expression.
ignore file added
Merge pull request #2 from samyam/master

One Dimensional AST Implementation