Fix local labels in macros to build with tpasm 1.6

Some version of tpasm between 1.2 and 1.6 changed how local labels
inside macros are handled. Now a local label inside a macro must be
prefaced with "@" instead of ".".
Initial import of OISC demo
Initial import of C string library
Initial import of RPN virtual machine
Initial import of Stranded (game)
Initial import of cooperative multi-threading library
Initial import of setjmp/longjmp routines
Initial commit of atexit routine