h2oai/h2o-3

…adme to state that r2_stopping is no longer supported and ignored if set (#349)

add backslashes for special characters in gbm booklet so it wont break

fixed typo that broke booklet build

updated the api help string so that it is clear r2 stopping is no longer used, but was previously used to making trees. This commit will affect the help string for GBM and DRF since it is in the SharedTreeV3.java file