document the date format string

I assumed the format string was related to strftime except all of the
fields looked really weird.  After digging in the code, this string is
actually used with php's date().  Add a note for this so other people
can jump quickly to the relevant documentation (which is useful for
non-php peeps who have no idea what this is).
Merge pull request #194 from vapier/master

document the date preference format string
adjust previous patch phrasing a bit
googlereaderkeys: add o/enter/? keys like Google Reader
Merge pull request #195 from vapier/master

more Google Reader keys
Revert "remove floicon because its author is a colossal shitlord (http://tt-rss.org/forum/viewtopic.php?f=1&t=2055&p=10824#p10822)"

This reverts commit dce5037888968788518dfdb6b1c29f3863238b92.
add a placeholder where floicon might be added if needed, still keep it
off trunk re: author being a shitlord