File based backend (#53, @nbenn).
Fix bugs in key_set() on Linux (#43, #51).
Windows: support non-ascii characters and spaces in key_list() service and keyring (#48, #49, @javierluraschi).
Add support for listing service keys for env backend (#58, @javierluraschi).
keyring is now compatible with R 3.1.x and R 3.2.x.
libsecret is now optional on Linux. If not available, keyring is built without the Secret Service backend (#55).
Fix the get_raw() method on Windows.
Windows: get() tries the UTF-16LE encoding if the sting has embedded zero bytes. This allows getting secrets that were set in Credential Manager (#56).
Windows: fix list() when some secrets have no : at all (these were probably set externally) (#44).
First public release.