Tidying "User Project" links

[elsiehupp]

I started on this because I ran into several dead links on the existing page, but then I got carried away.

Thus far I have been:

• Fixing dead links and reformatting links to distinguish between websites, GitHub repositories, etc.
• Reformatting to improve legibility on small screens (i.e. using narrower tables and not relying on table headers for platform names)
• Reorganizing miscategorized entries
• Simplifying description grammar and editing it for consistency
• Alphabetizing sub-list entries

This is a work in progress, so please do respond with any thoughts on how I should continue working on it.

[elsiehupp]

(Yes, I know this is kind of a mess in its current state. I just want to put this up here so I can set it aside and go to bed.)

[kuraga]

@elsiehupp , ping.