change notation of ast
change structure of the proj
add todo list
add subst function and occurs check
unify alpha version ok, eliminate rule needs revision
add more types for prolog constructs
Merge pull request #1 from xiaohe27/unification

Unification
modify the projCommon.ml
Merge branch 'master' of https://github.com/xiaohe27/PrologInOcaml into lexer
Get the latest thing from master branch
add glue.ml