TODO: call/cc broken with or with SCHEME_STACK, also in tinyscheme

- major size optimisations
  - struct layout for both typical CISC and RISC cpus.
  - optional error messages.
  - optional error checking.
  - cell size reduced by not storing both float and int forms of a number,
  - major dependency optimisations (no stdio etc.)
- faster and vastly simpler vector memory management (execution speed
  is roughly twice faster than tinyscheme when optimised for size, and 2.5
  times faster when optimised for speed).
  - no need for consecutive cells
  - more compact and faster vectors.
  - resizable vectors (not exposed yet)
- faster environment implementation, not hashed by name but by symbol address.
- simpler cell memory management, only one block
- much faster call stack implementation, fully supporting continuations,
  while greatly reducing cell thrashing, thus fewer gc's and overall
  much faster execution.
- allow full 32 bit size range for strings and vectors.
- made ports optional.
- made error checking and error strings optional.
- ripped out features: dynamic loading, nonstandard C targets.
- fix numerous ISO C violations (mostly _ namespace).
- fix numerous uninitialised value violations.
- fix some bufer overflows (mostly relying on _sprintf terminating with 0).
- fix numerous sign/truncation problems.
- remove limit of 65535 args maximum.
- move ~5kb opcode table into read-only segemnt, saves 5kb rss.
- reduce ~5kb opcode table to 1.2kb.
- subnormals are no longer flushed to zero in some comparisons.

TODO: atom names starting with dot cannot currently be parsed due to a tinyscheme bug.