Introduce ConfigKey

A ConfigKey has a config path (String) and a type parameter indicating the type that should be extracted from that path.
Bump version to 0.2.1-SNAPSHOT
Add ValueReader.localized
Upgrade to Scala 2.10.2
Add to ScalaDoc for ValueReader.localized
Merge branch 'develop'

Conflicts:
	version.sbt
Upgrade version number in README