Add Kane benchmark using SymPy and CSymPy
More efficient Add::diff() implementation
Add small optimization
Add another test for diff()
Fix a bug with handling numbers in Add::diff()

The test was added in the previous patch
Speedup Add::subs()
Speedup Mul::subs()
Fix the 1/x bug and add a test
Add few expand tests
Turn on stacktraces in Python wrappers
Fix the expand() bug
Make Add::as_coef_term() a static method
Add a TODO item
Simplify and fix Mul::expand_two()
Move as_coef_term() into Add
Optimize sin/cos subs()
Optimize Add::subs()
Optimize Mul::subs()
Optimize Pow::subs()
Merge pull request #87 from certik/kane

Add Kane benchmark