libgpkg: new formula; SQLite3 extension for OGC GeoPackage implementation

Early, but fairly complete, library support for the proposed [OGC GeoPackage](http://www.ogcnetwork.net/geopackage), a significant new open-source geospatial standard.

See also [`libgpkg` wiki](https://bitbucket.org/luciad/libgpkg/wiki/Home).

Formula [reviewed by developer](https://bitbucket.org/luciad/libgpkg/issue/2) of lib.