debug prints when a global stack is realloc'ed
realloc pic->irep when exhausted
load_stdlib releases arena objects every time evaluating exprssion
protect more objects during expansion
less memory usage of pic_reverse
remove unnecessary protect
fix broken pic_type_repr
alloc stacks by calloc, not malloc
add new compilation flag GC_DEBUG_DETAIL
print propagated error messages when stdlib failed to build
add overflow guards to some global stacks (or value pools)
[workaround] add stack overflow detector
rewrite gc!
shrink default heap size