Allow fully-yanked gems to be unyanked by the original owner

This still allows for a new user to swoop in and claim the gem by pushing their own version. Doing so would delete the previous ownership.
Refactor to yank a version directly rather than through its gem
Patch existing find_or_initialize_version_from_spec to make size an optional parameter.
size_in_kilobytes -> number_to_human_size
Change to cleaner syntax.
Add size to versions.
brought Chris's patch up to date and added a script to calculate sizes for existing gems
cleaned up Version#size interface
smoothed out size interfaces in Pusher and Rubygem
Add Badge link to Rubygem pages
Merge branch 'master' of git://github.com/rubygems/rubygems.org
Add test for badge_link helper
Merge branch 'master' of git://github.com/rubygems/rubygems.org
allow user handles with a length between 1 and 40 characters (similar to GitHub)
change user handle validation to require at least two characters
add non-prefixed border-radius property
add non-prefixed box-shadow property
add non prefixed linear-gradient function
remove vendor prefixes for border-radius
remove vendor prefixes for box-shadow