Merge tag '1.5.5' into develop

* Added StringComparitor::isIn() for making sure that a string is in a list of specified values
* Fixed HttpClientRequest::getEncodedBody() to use http_build_query and add support for bodies that contain nested arrays
New: import of RateLib
Merge remote-tracking branch 'origin/develop' into develop
Version bump
Merge branch 'release/1.6.0'