Initial commit of the new erli backend.

Contains a rough implementation of a first resource along with the
necessary storage and utility API as well as overall modelling
required to compile/run the application.
Fixes issues after an initial dialyzer run.
Improves the rebar configuration and fixes webmachine logging in preparation of CT.
Cleans up the webmachine configuration.
Fixes issues related to dispatch.conf path for testing with ct.
Fixes a bug in the content-range header for target collections.
Fixes pattern matching for the options resource call.
Fixes the implementation of the Content-Range header by moving it out of the resource into utils.
Adds an implementation of is_url/1.
Unified the structure of json data returned by the resource.
Cleans up POST data processing in the target resource.
Adds an initial implementation for form validation.
Fixes structure of the error message for required fields.
Fixes a couple of logic bug related to target resource creation.
Fixes an issue with the return of create/2 when a conflict occurs for targets.
Replaces all occurrences of posts with targets in json returned by the target resource.
Fixes naming of the initializing module.
Fixes an issue with etag generation for collections and makes naming more intuitive at one point in utils.
Fixes two bugs with range header parsing.
Adds cover support to ct.