additional changes as follows:
* LTRFeatureLoggerTransformerFactory:
** feature values cache name configurable (instead of hard-coded value that needs to match solrconfig.xml configuration)
** javadocs (example and parameters)
* CSV FeatureLogger:
** removed delimiter and separator assumptions in tests
** changed delimiter and separator (from "key:val;key:val" to "key=val,key=val")
** configurable (key value) delimiter and (features) separator
* JSON FeatureLogger:
** defer support for this (removing MapFeatureLogger class)
* adds 'training libraries' to (Linear|MultipleAdditiveTrees)Model javadocs
(Diego Ceccarelli, Michael Nilsson, Christine Poerschke)
