Convert ordered factors to character.

writeOGR fails with ordered factors.
Add method for SpatialPointsDataFrame
Merge pull request #9 from ateucher/spatial_methods

Convert ordered factors to character, add SpatialPointsDataFrame method
added @ateucher as pkg author
ignore geojson files if any in the pkg
fixed missing ... in to_geojson internal fxn, fxied rbuildignore
remove funky character hiding in the documentation