Eliminate compiler warnings

[momohatt]

Currently, building Egison code with -Wall flag issues a lot of warnings. We should deal with these warnings for improving code sanity.

cf. https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/using-warnings.html

[momohatt]

• Eliminate -Wno-incomplete-patterns
• Eliminate -Wno-unused-matches
• (Optional) Eliminate warnings from Parser.hs, which is suppressed for now

I'm not sure if we should also try to eliminate -Wno-name-shadowing.

[stmtk1]

there are only a few warnings, "-Wunused-matches" and "-Wunused-local-binds". I think these warnings are not critical. If these should be eliminate, I want to do.

[momohatt]

Sure, thanks. But you'll have to fix sweet-egison (not egison itself) to remove the -Wunused-local-binds warnings in Math/Rewrite.hs. You can ignore them if you want to.

[stmtk1]

I aware removing -Wunused-local-binds is very difficult. So I will try eliminating another warning