add a utility class for the ROCKTAB keyword

this one is a bit more complicated than a plain SimpleTable as the
number of columns depends on the deck. (to be precise, it depends on
the presence of the RKTRMDIR keyword which is also added in this
patch.)
add a utility class to handle ROCK tables

So far, this only considers Eclipse R100...
Merge pull request #111 from andlaus/better_rocktab

add a utility class for the ROCKTAB keyword