Convert lookahead buffer to array
Convert lookahead buffer to array

This saves a significant number of memory allocations, from not doing realloc
with every token being added to the buffer.

Still need to support rewind to act like a queue, so array abstraction is
somewhat broken in this case.

larmel/c-compiler,larmel/lacc,larmel/c-compiler,larmel/lacc,larmel/c-compiler