More Expr grammer

key-slices, nested expr in grammer
Added class to run both parsers together on local files  and comparing the results.
Ignore Jetbrains IDEA files in git
Parser bug fix. Fixing encoding of large enums (> 32k values) + const chunks with NAs (test for NAs was missing so it was being encoded as constant numeric chunk and thus losing/replacing the NAs)
prefix function ops

also mul/div/isNA
Merge branch 'master' of github.com:0xdata/h2o
Added system.exit to DatasetCompare main for Tom.
Merge branch 'master' of github.com:0xdata/h2o
Changed PCA score API to FluidVecs
Merge branch 'master' of https://github.com/0xdata/h2o
Supporting branch name env. param. in get_s3 script.
Merge remote-tracking branch 'origin/master' into vers