Updated attribute handling

* Using Occi::Core::Attributes
* Unified attribute handling, not just hardcoded occi.core.title
* Attribute type handling still unclear, everything is a String
Fixed a minor typo in ROF
Better rendering into JSON and pretty JSON
Added fine-grained control over log lvls
Fixed JSON rendering of multiple resources
Bump to version 4.2.0.beta.3
Merge pull request #19 from arax/attr_fix

Fixes attribute handling and some minor stuff