Allow more tokens in the assembler.

Allow more tokens in the assembler.

I need this so I can add more %token lines to mach/powerpc/as/mach2.c

The assembler's tempfile encoded each token in a byte.  This only
worked with tokens 0 to 127 and 256 and 383.  If a token 384 or higher
existed, the assembler stopped working.  I need tokens 384 and higher.

I change the token encoding to a 2-byte little-endian integer.  I also
change a byte in the string encoding.