Faster factorial, and gamma implemented with tests.
The tests now work, but still have use Math.PI.
No longer change the config state; now using new created state in test cases.
Use the new cosh or sinh for complex numbers.
Merge branch 'develop' of https://github.com/josdejong/mathjs into gamma_factorial
Updated use of bigPi, and adjusted the test cases as well.
Merge branch 'develop' of https://github.com/josdejong/mathjs into gamma_factorial
Removed BigNumber bad implementation. Also, cleaned up the code, switched the coefficients for Lanczos, and added extended Stirling approx.
Failed at adding gamma to the parser (attempted to add 1 to all the values while using gamma, then tried to wierdly overload ! token). I added BigNumber integer support for gamma to allow more flexibility when integrating it into the parser (if that is something that is done).
Merge pull request #245 from BigFav/gamma_factorial

Gamma function (no BigNumber, arbitrary-precision), and updated factorial.