add some documentation about the structure of CODE_SRC entries as well as SRC_FILENAME and SRC_FUNCNAME
typefn and pretty printer for T_CODE objects
export the vector marker, sweeper, hasher, and such (many objects are derived from vectors)
__resize_vmcode can now handle resizing initially empty code
add function to make an empty code generation context
prototypes for code generation functions
clean up types, and make the vector typefns publicly accessible