Added first draft of ggmap

@sckott can you give me some feedback if this is the right direction? It will help me proceed as I polish up the fn.
added noRd tags to internal fns.
Resolved conflcit in occ()
Added ecoengine to install list.
Deleted duplicate ggmap file
Minor edit: formatting.
Fixed issue raised by doc_check()
ggmap work correctly with various occ results
Updated documentation and namespaces
Added page breaks to install code block.
Added first draft of unit tests. #28
Merge pull request #27 from ropensci/ggplot-integration

Ggplot integration