rappdirs 0.3.1

Minor R CMD check and test fixes.

rappdirs 0.3.0

• first CRAN release
• xxx_dir() functions only use version when appname is not null
• docs: basic package docs (?rappdirs)
• docs: clarify primary purpose of os argument in xxx_dir() i.e. testing
• fix typo in function name in README.md (app_dirs -> app_dir)
• dev: add travis continuous integration
• dev: add rstudio project
• dev: update to roxygen2 v4.0.1