Fix in answer to changes in R's C-API (see rpy2 issue and resolution
https://bitbucket.org/lgautier/rpy2/issue/150/rpy2-crashes-upon-import-with-r-302
)
- Various fixes for environments
- Added a method "keys"
- Tentative type "RPackage"
- Function "rimport" (pretty much like "importr()" in rpy2, but following
  the naming in PyCall ("pyimport")