clean the interface, get rid of dependency on Unix
ready to switch to the constraints by default
clean
add cold/fan.ml
make default to add type annotations
fix a bug in str_quot
snapshot the changes to cold
ocamllex backend seems to work
PR:01
nasty lexing problem see TRACKER 01
built in lexer seems to work.
Something to notice:
   now lexer follows ocaml's own lex convention:
   that said ,   *|  is not good, you have to write it as * |
remove Ulexer