Work in progress. First basic version of a converter hierarchy and a working implementation that delegates to Spray-Json

only the "read" side has been implemented so far
Some formatting
Added a basic StringRiakValueConverter
Renamed the SprayJsonConverter
Got rid of the old raw String version of bucket.store() and replaced it with one that uses the converter infrastructure, which contains a basic string converter
Added an extra apply overload for RiakValue for the common converter case of knowing the content and the content type but not having any other meta-data
Implemented the write-side of the SprayJsonConverter
Added a license file and some very basic README content
Merge remote-tracking branch 'origin/converters'