Mostly working prototype of a feed summary screen (FEEDBACK REQUESTED)

[mnp]

Sketch based on reddit conversation with @skeeto for a feed summary that shows you a screen by feed (with counts and dates) instead of by article.

I've hooked into the toplevel elfeed using a defcustom elfeed-summary-as-top-level, such that if t, you get a selection flow like this:

"work" ---(M-x elfeed)---> feed summary ---(Ret)---> search ---(Ret)---> article/entry

and then a reverse flow popping back up

"back to work"  <---(Q)--- feed summary <---(Q)--- search <---(Q)--- article/entry 

TODO:

• desktop support?
• hooks?
• bookmarks support?
• user might want to configure columns