Add compiled/cached MachineCode

[OneOfOne]

$ /bin/go test -run=xxxx -bench=Parse -benchmem -benchtime 5s

goos: linux
goarch: amd64
pkg: github.com/bspaans/jit-compiler/ir
cpu: AMD Ryzen Threadripper 2950X 16-Core Processor 
Benchmark_Parse/No-SSA/No-Cache-32         	      19	 307234346 ns/op	188360269 B/op	 6094822 allocs/op
Benchmark_Parse/SSA/Cache-32               	  411292	     15084 ns/op	       0 B/op	       0 allocs/op
Benchmark_Parse/SSA/No-Cache-32            	      18	 335270616 ns/op	188984950 B/op	 6107401 allocs/op
Benchmark_Parse/No-SSA/Cache-32            	  401347	     15060 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/bspaans/jit-compiler/ir	27.835s

[MatejMagat305]

why not be this improvements accept?