Xutils

- Add `find_config_file` to find the configuration file.
- Add the utility functions, `which`.
- Add the module `messager`.
- Let `check_output` be compatible for some arguments in Python 2 & 3.
- Add the default WSGI Server `WSGIServer`.
- Add the method `respond` for `Resource`.
- Add the customized `Router` for wsgi.
- Change `Application` to the alias of `falcon.API`.
- Add the function `get_exception_handler` to get a default exception of `falcon.API`.
- Replace the method `add_route ` of `falcon.API`.
- Fix some bugs.

- Add `wsgi.Resource`

- Add the module `wsgi` based on `falcon`.

- Add the module `Circuit Breaker`.
- Add the module `Call Retry`.
- Add the module `Lifecycle Manager`.
- Add the module `Resource Pool Manager`.
- Add the module `Process Manager`.
- Add the module `Rate Limit`.
- Add the module `Resource Lock`.
- Add the module `sqlalchemy` to support Database.