ggpath 1.0.2

• Invalid paths no longer result in an error. Instead, ggpath will warn the user and insert an empty grob.
• Minor adjustment to the format of lists in the documentation to avoid check problems in an upcoming R release.
• Added new theme element element_raster() that allows custom images in ggplot backgrounds. (#9)
• Drop dependency to package rappdirs and create an optional user cache with base R's implementation. To support older R versions, ggpath now imports the backports package. (#10)