Exec2 supporting row based apply. In progress. Tests to be added.

ex:

apply(h.hex, 1, min)
apply(h.hex, 1, max)
apply(h.hex, 1, sum)
apply(h.hex, 1, c)
apply(h.hex, 1, function(x){c(min(x), max(x)})
Merge branch 'master' of github.com:0xdata/h2o