[ocaml] ignore eclipse project files
[ocaml] implement sftype AST & domain (not complete)
[ocaml] implement type algebra & valuation functions
[ocaml] fix bugs
[ocaml] rename <= & < operators with ref_prefixeq_ref & ref_prefix_ref
[ocaml] fix bugs on sfdomain.ml; implement inherit type environment for prototypes; refactor codes
[ocaml] merge sftype to typesystem
[ocaml] rename type syntax
[ocaml] rename sfast.ml -> sfsyntax.ml