Improvements from my personal branch

[Quetzalcoatless]

A few years ago I established a personal branch of FanFictionReader with some major improvements over the original:

• The biggest change, a vast improvement in downloader performance with large libraries. There were several changes made, with the end result being that a full library update of 3000 stories went from taking 40-90 minutes down to only 5-20 depending on how many stories had updates, and whether you have the app set to redownload all chapters or not.
• Errors will randomly pop up while checking for updates on FFN's site, usually a 503 that'd be fixed by a refresh. In the released version the app will cancel the update after encountering just one of these. In my branch three errors must occur in a row for the update to fail, something that is vanishingly unlikely if FFN is not down.
• Chapter compression has been added as an option. A large library can take up multiple gigabytes, so this can save quite a bit of room. Unfortunately it's not retroactive (and even a PC would take a very long time to compress the tens of thousands of files in the library, so doing it on demand isn't practical), so the benefits would only apply to updated/newly downloaded chapters. The menu support for this one isn't finished.
• A filter when browsing authors to only show WIP/complete stories. This one still needs work, as an entire page being filtered out will break the next page button.

Unfortunately I don't have the time to merge in master's changes, make, and test several proper pull request these days - I don't even have Android Studio set up right now - so I'm posting this as an issue in the hopes that someone has the time to pull in my changes and make sure they work with the way the main branch has developed, and add the polish I didn't feel was necessary for a personal branch.