Creating tests for the gauss_quad.jl functions.

I found a problem in wgj. It doesn't work for large Q.
Problems with factorial(Q) for Q>20.

I replaced it with gamma(Q+1).
Forgot to remove debugging stuff from wgj.
Created functions that implement gamma ratios.

rgammanm -> gamma(x + n)/gamma(x + m)
rgammaxy -> gamma(x + n)/gamma(y + n)
rgammaxnym -> gamma(x + n) / gamma(y + m)

These functions are not being used but it is interesting and could be useful.
I should probably try to implement the ration functions defined on boost:

gamma(a) / gamma(b) or gamma(a) / gamma(a + delta).
Working on docs (README.md).