[gen] Introduce a new relaxation/edge/atom parser in diy tool.

[ShaleXIONG]

This is a first phrase to rework on the diy* lexer and parser on input relaxations or cycles. In this pull request we introduce a more conventional way, that is, (1) new lexer.mll tokenises input to an AST, specifically type t in new ast.ml and (2) new parser.mly parses the AST to internal data structure. Note that we keep the old lexutil.mll for backward compatibility, and this file will be remove for next phrase.
In the Ast.t, individual primitive relaxation is represented by One of string. The consequence of relaxation is represented by Seq of t list; this corresponds to , syntax or in some situation, white space. For example diyone7 PosWR PosRR Fri is equivalent to diyone7 PosWR,PosRR,Fri. We also introduce a Choice contractor, together with a new syntax |. For example PosWR|DpAddrdW means either PosWR or DpAddrdW. This can be used in diycross7 and diy7. In diyone7, although it will be parsed however an error occurs due to input is not a precise one cycle. The future plan is to gradually deprecates only diycross7 syntax.
for example diycross7 Po,DpAddr Rfi,Fri,Coi is in fact means diycross7 Po|DpAddr Rfi|Fri|Coi.
Last, Given all the chances above, we unify the paring process cross three diy* tools. Previously different diy* has different parsing path and the actual code are in different files. Now the main passing function unifies at parse_expand_relax and parse_expand_relaxs in relax.ml. The future plan is to remove the Ppo type as it is only used in PPCCompile_gen.ml as a special wildcard. However the current parsing is after we flatten the Ast.t to a string list list, so we can hook to the existing parsing functions. The future plan is to parametrise the type Ast.t, so we can directly parse on the Ast.t.