Add Combine/Merge functionality for Word

Word has a "Merge" or "Combine" mode as well diff/compare (at least in the latest versions).

Propose extending the tool to accept a merge mode in addition to diff which will use the Word Combine mode instead of Compare. This appears to accept multiple files so it could be either 2 or 3-way merge (thus could be easily configured to work with git in the same way diff is).

[Here is a Microsoft page explaining how to use the Merge function](https://support.office.com/en-us/article/combine-documents-f8f07f09-4461-4376-b041-89ad67412cfe). Wouldn't it be nice if MS had command-line arguments for these functions?