Reintroduce ``cache=True`` for jit compiler in support_enumeration

The cache was switched off due to an issue with ``numba``. 

https://github.com/QuantEcon/QuantEcon.py/pull/157

This should be reactivated once https://github.com/numba/numba/pull/2286 is merged and included in the base ``numba`` version of the anaconda distribution. 