Demonstration of a black-scholes model in C

Note that there are two models, a pure Monte Carlo implementation
and the closed form black scholes equation.

Recommended number of simulations is 100,000,000 for Gamma convergence, the
other Greeks converge by 1,000,000.

TODO:
 1. Find a C implementation for Sobol sequence so that Gamma convergence
    is faster
 2. Tests...