Up version to 5.2.0.
Don't crash when getters and setters in JavaScript.

Make the RKellyAdapter correctly adapt the getters/setters into
properties of "get" and "set" kind.
Detect JS getters/setters as properties.

But only when documented with a doc-comment.  Completely ignore
getters/setters when auto-detecting class members.

Fixes #441
Fix RKellyAdapter tests for escape chars in Ruby 2.0.

Force RKellyAdapter spec source to ASCII encoding.
Include Ruby 2.0.0 to Travis config file.
Don't make Object.defineProperty with get/set into readonly.

Only data properties can have the writable flag, accessor properties
can't.

Fixes #444
Turn Object.defineProperty with only getter into readonly.

Refs #444