Tidy up includes
Add ci_char_traits
New http::client_session for making requests:
- Add 10,000 popular URL data set for unit tests
Fix clang/travis, prefer static libs when BOOST_ROOT is set.
Report whether a ledger is validated:
This addresses https://ripplelabs.atlassian.net/browse/RIPD-275
Use Json::StaticString to improve performance.
Use inject_error instead of manually adding errors.
Fix a few warnings