Notes for work to do on this branch:

- add constant for max size obj on stack (maybe limit * 2?)
- make vector - alloc on heap if size of elements > max size limit
  (need to make this function as potentially blocking? probably, but maybe leave a TODO for now)
- add heap type ID to heap struct
- add a huge obj heap
  - this heap will only allocate objects of size >= max stack obj size
  - make sure to allocate obj size + alignment
  - each page is just one obj, will free page when obj is freed (as part of sweep)
- initially, work will allow the gcbench from larceny to work