Setting version to 7.1.0-M2
Setting version to 7.1.0-SNAPSHOT
Class-ify ==>>.
scalaJSONObjectPLens and scalaJSONArrayPLens is deprecated

because `scala.util.parsing.json` is deprecated from Scala2.11
https://github.com/scala/scala/commit/3e1a075a7e8b9178
tweak scaladoc. add scalaz.Optional
Merge pull request #454 from xuwei-k/deprecated-std-json

scalaJSONObjectPLens and scalaJSONArrayPLens is deprecated
update DeveloperGuide