fcio.c is not included in the clang/ dir anyways

This introduces 16 and 32 bit versions of
POKE/PEEK in order to reduce the number of
ifdefs.

The restructures so that the root
directory contains `src/` and `include/`.
Compiler specific asm files are in src/cc65
and src/llvm respectively. This required updated
of the builds systems as well as instructions in
the README.

This to allow for other compilers like vbcc and kickc

vbcc can compile src/memory.c to no
need for special dir

Possible kickc specific assembler code
moves to src/kickc. Main headers seem to
be compatible.

…unify-cc65-clang