update command pages using wp-cli/wp-cli@7cea2ca5e0b8a79ebcc70d476c2ab5da310f2433
unbold dt tag; makes '...' more legible
remove pages for old commands

keep references for plugin|theme update-all, because they were used as
examples in a lot of presentations
update commands pages after wp-cli/wp-cli@b6334de
avoid -- being converted to &ndash;

fixes wp-cli/wp-cli#808
add 0.12 release post
Merge pull request #25 from wp-cli/release-0.12

Release 0.12