fix infinite loop bug in env2heap
verify behaviour of test_heap_env
simple test for funargs
heap-based environments implemented
mechanism to move continuations to the heap
remove useless creation of pairwise function value
add proto for arc_callcc
save the function stack beginning location when making an env
define arc_callcc
add function stack pointer beginning for a thread
some tests for continuations and call/cc
the base virtual machine is complete!