Basic optimisation of interpreter loop

[aapoalas]

Analyse the most common interpreter instructions, reorder these to the top of the instructions loop and keep them inline as they are currently. All uncommon instructions should (probably) be dispatched through a secondary function which only ever does a switch on the instruction and then calls into a separate instruction handler function.

With this, we can play around with which instructions are "at the top" and get inlined, and which are "cold" and are always indirected.