Added the 'issueNumber' constant to the RCRequestKeys.
Added the 'title', 'titleStartsWith', 'issueNumber' and 'startYear' public properties to RCComicsFilter and improved its "parameters" private getter method to handle them.
Updated the version number inside the source code files to 0.7.3.
Updated the pod spec to 0.7.3.
Updated the current project version to 0.7.3.
Updated the CHANGES file with the changes description for version 0.7.3.