use is.finite() instead of !is.na() to protect against Inf/-Inf values in lat/lng
wip
Revert "wip"

This reverts commit 92219f89b5fa2d630e2fbab0b97df8762361b59c.
Introduce resolveFormula and derivePoints

Also export pointsData generics, this is for testing
Layer-specific data overrides; infer lat/lng

- Add data parameter to most layer functions
- Reverse order of lat/lng to lng/lat in most functions
- If lng and/or lat are NULL, infer spatial points from data if possible
- Change how data is stored; map$x$data means the data will be serialized
  and sent to the client, that's bad
- Add normalize.R examples, we can delete once this all shakes out
Baby steps towards better polygon inputs
Whoops, rect lat/lng can't be null (yet?)
Better validation, error messages
Remove unnecessary returns

I often use unnecessary returns for clarity but these
two are pretty egregious :)
Only print first class in error message
Merge pull request #12 from rstudio/refactor/spatial-args

Nicer handling of spatial args
Proper evaluation of formulae with spatial data frames
Replace <- with =
add sp to Suggests
cosmetic

ouch, backslashes hurt :-)
unused argument
make it possible to just provide plain numeric vectors as lat/lng to polygons/polylines, by converting these vectors to lists automatically internally