Use LinkedList for Stack Frames.

[soasme]

Inside the stack frame, the silent and space states are also cached so we don't need the heavy lift of using NeedSquash & NeedLoosen.

The performance optimization is significant:

Running #15 against the current HEAD (10x faster than #15):

time ./a.out
real	0m0.014s
user	0m0.006s
sys	0m0.004s

See callgrind output: https://gist.github.com/soasme/f31ea5f78420304a1b12b434a4a808e9