Set version to 0.23.0
Better diagnostics for SSL certificate failures
Remove obsolete support scripts
Build system improvements:

* Reduce console verbosity.
* Display configured build environment.
* Log build environment and commands in rippled-build.log.
* When compiling under Travis:
  - define TRAVIS_CI_BUILD for C and C++ code.
  - define RIPPLE_MASTER_BUILD for builds made against
    the official Ripple repository.
General beast improvements and fixes:
* New maybe_const_t alias for maybe_const
* New safe_bool using C++11 features
* Fix is_call_possible metafunction:
  - Works on empty argument lists
  - Works with reference types
beast::asio improvements
* New enable_wait_for_async for safe cleanup
* New memory_buffer, a managed asio compatible buffer
* shared_handler improvements:
  - Can be 'empty' (no stored handler).
  - Default constructible as 'empty'.
  - Safe evaluation in bool contexts, false==empty