Use pbkdf2 for the masterkey

Number of iterations should be adjusted
Just overwrite the store
Changelog: Only mention the things that are already done
Changelog: Mention the minitest update
Sort methods by loc
no underscores in filenames
Improved error handling
Typo
Speed up the test by monkey patching the amount of iterations
Totally more readable
Define BASE_PATH constant in safe.rb
Gemspec: Don't use an array for the license
Rewrote the README
Readme: Updated usage example