**Merged pull requests:**

- Finalize 1st draft of types and structs, add docs (#1) (@vlandau)
- Graph constructors and tests (#2) (@vlandau)
- Add methods for SimpleGraphs and associate tests (#3) (@vlandau)
- LightGraphs interface fixes, add more tests (#4) (@vlandau)
- LightGraphs => Graphs, GeoData => Rasters, some changes to type names (#5) (@vlandau)
- fix graphs interface for weighted graphs (#6) (@vlandau)
- Revert "fix graphs interface for weighted graphs" (#7) (@vlandau)