use lemon for parsing

src/snc/Makefile

src/snc/gen_ss_code.c

src/snc/gen_tables.c

src/snc/parse.c

src/snc/parse.h

src/snc/phase2.c

src/snc/snc.y

src/snc/snc_lex.l

src/snc/snc_main.c

src/snc/snc_main.h

src/snc/snl.lem

src/snc/token.h