Also make integer to size_t casts explicit rather than relying on
int32_t * sizeof(x) = size_t. This is kind of a personal preference for
this problem.
Because we use an amalgated build, feature
test macros should be set in a single file that
is included before any other headers, and is placed
at the top of the amalgamated build.
This should help address #81. Also hide janet_exit
and janet_assert, as they are really meant for internal usage.
I have not verified that this yet actually works with Rust's
bindgen.
Leave in issues with calling memcpy with size=0. If these
become a problem, will probably add a janet_memcpy as memcpy
is used so much in the code without 0 checks.
