The first public release. A self-hosted compiler for c0, a small systems
language with one type, the 64-bit integer, compiling straight to x86_64
assembly with no libc and no runtime behind it.

Everything here is bootstrapped. coff0.c builds the real compiler from
c0/coff.c0 once, and after that the compiler compiles itself, verified as a
genuine fixpoint three generations deep.

The language at this point has globals, functions up to 16 parameters,
recursion, block scoping with shadowing, short-circuiting logical operators,
break and continue, string and char and hex literals, buf[i] indexing,
function references and indirect calls, and include for splitting a program
across files.