Moved devel deps to Gemfile
Bumping rOCCI-api version to 4.2.0
Version bump to 4.2.0.beta.1
Updated argument parsing, more consistent

* Changed `attributes` to `attribute`
* `attribute` can now be used multiple times or with commas
* `link` can now be used multiple times or with commas
* `mixin` can now be used multiple times or with commas
Added custom formatter errors
Major changes in output rendering and helpers
There is no #merge! for Occi::Core::Resources
Version bump to 4.2.0.beta.2
Empty arrays are allowed in the OutputFactory
Fixed output formatting for mixins and resources
Updated rOCCI-api to 4.2.0.beta.2
Updated mixin handling (new rOCCI-api)
Listing only relevant resources in intr. mode
Adding support for identifiers to ListHelper
Minor fixes, resetting values in intr. mode
Identifier support for DescribeHelper
Improved mixin handling
Fixed logging and mixin handling in CreateHelper
Merge pull request #16 from arax/new_core_api

Staging for 4.2.0 (beta.1 & beta.2)