Merge tag '3.1.0' into develop

3.1.0
start 3.2.0
Ad GUI and Ad Model updates.
Default packages.
Update default form factors.
Learn more button is now passed the ClickThrough url from the vmap.
cleaned up element structure.
vmapURL is a jsonp url, so don't go through the proxy.
stringifying css instead of doing it manually
set width and height of placeholder so css isn't required.
Auto-creating players for where data-auto-create exists.
Updating GUI path.
update README.md
don't check for width/height isNaN, Zepto/jQuery will do that for you.
don't hide the native controls while the user is scrubbing, it causes the player to break.
handle a seek time of undefined better.
fixed reading of data-attributes that broke a few builds ago.
Math.ceil time so we don't see your ad will resume in 0.
Best practice for underscore, don't _.bindAll(this) without method names.
unicorn references renamed to vmap.
fixed vmap tests.
remove tap output for now from testem tests.
use grunt testem 0.3.6
message in startIndex into player if it's specified in config
History.md for 3.2.0
Merge branch 'release/3.2.0'