Added getKeyword() method to Section class.
Added new keywords for parsing cartesian grid.
Added ERT dependency in build of opm-parser.
Added class EclipseGrid with constructor for cartesian grid from deck.
Changed cornerpoint related keywords to use FLOAT.
Added float data accessors.
Added ability to create EclipseGrid from cornerpoint keywords.
Merge pull request #157 from joakim-hove/OPM-75-create-grid

Opm 75 create grid