Massive restructuring of lexing and parsing (NASM-compatible parser).

Massive restructuring of lexing and parsing (NASM-compatible parser).
Bugzilla Bug#3.  Not all instructions are parsed yet, so this is actually a
minor feature regression from the user side, but this commit lays the framework
for much easier additions of new assembler syntaxes and architectures.  The
re2c tool is now used to generate the lexers, as it's much more flexibly
function-oriented than lex.
 - nasm-bison.y is a repocopy+modify of nasm/bison.y.in.
 - x86arch.h now includes all of x86-int.h

svn path=/trunk/yasm/; revision=670