A lof of small things

[superbobry]

• Tabulated 'lnfactorial' for small inputs
• Switched to -O3 for compiling Cythong extension
• Replaced hand-rolled lngamma with 'lgamma' from libc
• Renamed C & G to K & N to match Wikipedia notation
• Removed imin2 and imax2, builtin min/max do exactly the same
• Marked all of the functions as nogil, so they can be computed in parallel in multiple threads
• Updated tests to check all three alternatives

[brentp]

LGTM, though the reason for imin2/imax2 was because those are fast inlined versions that avoid the overhead of the python min and max functions. Since those aren't in tight loops, I guess simplicity is preferable here.

[superbobry]

I've checked the code generated by Cython. The line

cdef int lm = max(0, n - (N - K))

is translated to

__pyx_t_1 = (__pyx_v_n - (__pyx_v_N - __pyx_v_K));
__pyx_t_2 = 0;
if (((__pyx_t_1 > __pyx_t_2) != 0)) {
  __pyx_t_3 = __pyx_t_1;
} else {
  __pyx_t_3 = __pyx_t_2;
}
__pyx_v_lm = __pyx_t_3;

Similarly for min.

[brentp]

sweet! thanks