add quote, macro, variable rebinding, struct and etc to syntax_tools

I'm invited by Richard Carlsson to contribute some of features in my
project https://github.com/slepher/astranaut to syntax_tools.

Theses are mainly four step features of this application
* Monad related modules (from [erlando](https://github.com/slepher/erlando),
but erlando deps on this application, so it's a minimal implementation)
* AST traverse function
* Quote: Elixir style quote
* Macro: Elixir style macro

These features make code look cleaner.
* Compile Meta: get compiled data like errors, warnings, forms at runtime,
developed for test this application.
* Do: do comprehension syntax from erlando

Other features are
* Rebinding: Elixir style variable binding.
* Struct: Elixir style Struct
* Disable TCO: disable Tail Call Optimization to get more information in
exceptions.

Here is my plan:
* commit ast_traverse, quote, macro with one or three pr
* commit rebinding and struct with two pr.
* I'm not a native english speaker, some of function and options name maybe
improperly, which should be renamed
* for not change the old codes,  rename module begins with astranaut_ to
erl_syntax_

Any suggestions?
You could reply to this email or comment on this issue
https://github.com/slepher/astranaut/issues/11.