Merge branch 'vm-refactor': refactor block construction
compiler: fix bugs in calling closures
add counter example
VM: split length_t and id_t from word_t; refactor anything that uses them
VM: generate pointer maps for Meta and Package
VM: make the location of block "length" fields configurable

- This removes the need for custom sizes for Free, Stack, and
  Function.
- Length can either be 32-bit or word-sized.
VM: wrap pointer members in new Ptr class
VM: check for overflow on string concatentation
VM: remove remaining -inl.h headers
VM: remove unused List and Map classes
VM: replace static cast functions with single template
VM: add release configuration