interpreter: boost execution speed by converting instruction translation to O(1)
interpreter: boost execution speed by converting instruction translation to O(1)

Instructions were being expensively converted to a method name and then
executed every time the program flow needed them, effectively becoming a
processor hog O(n^n). Moving out of line this process makes for orders of
magnitude better performance.

This has been benchmarked against stock version 0.2.1:

alex@quadcore:$ time ookie prime.ook
Primes up to: 60
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59

real	7m54.484s
user	7m52.780s
sys	0m0.200s

With this patch applied:

alex@quadcore:$ time ookie prime.ook
Primes up to: 60
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59

real	0m35.995s
user	0m35.500s
sys	0m0.020s

unleashed/ookie