Wiki updates

[David Sterba]

Hi,

I've updated the Status page and synced the manual pages from btrfs-progs git.

The status of various features is split to one more column, Performance.
There's a section for each 'mostly OK' status below the table and linked from
the note. This will hopefully be more understandable than just a single color
table cell.

Please note that the page is locked, so either drop me a mail or use the talk
page to suggest edits.