Git Compare and dist-diffs ant targets

Hey Jim,

I've finished up the targets/tasks that compare a custom git branch to master. I'll preview how it works:

1. Navigate to the appropriate dir (the targets work in *develop/learning-paths*, *develop/tutorials*, *use/social-office*, and *use/using-liferay-portal*.
2. Run *ant compare-with-master -Dcompare=YOUR_GIT_BRANCH_YOU_WANT_TO_COMPARE_TO_MASTER*. This creates a *git-modified-list.txt* file in your dir, listing all additions/modifications on your personal (origin) branch, compared to your master (origin) branch.
3. Run *ant dist-diffs*. This zips the diffs listed in the *git-modified-list.txt* file into a zip file, which will be located in the *dist* dir.

From my brief testing, it handles multiple images and articles, even if they're from the same folder. Let me know if there is anything you'd like me to add/edit/remove in this process. Thanks!

https://issues.liferay.com/browse/LRDOCS-1385