Ability to create diff files

[ajeanmahoney]

The current tools the RPC uses for creating HTML diff files of two versions of Internet-Draft text files are the command-line tools htmlwdiff, which creates inline diffs, and rfcdiff, which creates side-by-side diffs. The htmlwdiff script that the RPC uses is different from the bap htmlwdiff script in that it can strip headers and footers, end-of-line whitespace and \r (CR).

The software should provide the ability to create both side-by-side and inline diff files in HTML format. The user should be able to view and to save this file.

An online version of the diff functionality could create a diff file using the latest version of the Internet-Draft text file found in datatracker and the latest version of the text output created by the editing software as input.

However, the ability to create diff files using input that is not found in datatracker is also a use case: sometimes authors provide updated drafts that have not be uploaded, and April 1 drafts are never in datatracker. The user should be able to select a local file as the 'old' file to compare against.