Merge pull request #36 from carrot/allow-blank-button-text

Allow for blank button text.
Center Twitter and Google+ Popups. Closes #33
Merge pull request #42 from brunolazzaro/master

Centered Twitter and Google+ Popups when they are opened.
Update readme.md
Merge pull request #43 from girasquid/patch-1

Fix typo
release 0.0.4 :shipit:
merge