Add cmake support for various drivers

This change adds support for:
* rs2: RadarSat2 XML
* ilwis: ILWIS Raster Map
* sgi: SGI Image Format
* srtmhgt: SRTM HGT Format
* leveller: Daylon Leveller Heightfield
* terragen: Terragen Heightfield
* fit: FIT
* rmf: Raster Matrix Format
* gsg: Golden Software
Merge pull request #21 from simonsonc/various

Add cmake support for various drivers