This splits up the module level optimisation passes as follows:

1. Runs a cheap pass to inline across the module, this in an
   attempt to bring as many refops into the same function as
   possible.
2. Runs the reference count pruning pass.
3. Runs the full optimisation suite, this should discover many
   more opportunities for optimisation as a result of the inline
   and refop prune.

Closes numba#5033

As title, results in similar runtime performance as O2 but at much
cheaper compile time cost.

…ectorization_1

As title