Added method EclipseGrid::resetACTNUM()
Added EclipseGrid::fwriteEGRID

In addition an new constructor based on an existing binary GRID/EGRID
file.
Merge pull request #268 from joakim-hove/EclipseGrid-reset-actnum

Eclipse grid reset actnum
Added c_ptr() method to EclipseGrid
Merge pull request #269 from joakim-hove/master

Added c_ptr() method to EclipseGrid