Update OS X script to follow style guide

Every other function or script in the repository uses a function call,
so update the ./bin/osxdefaults script to follow suit and the dotfiles
install script to call it accordingly.

Issue: #12
Update osxdefaults with more settings

Combine @mathiasbynens[1][osx] and @necolas[2][osxdefaults] dotfiles
scripts with my own personal tastes.

[osx]: https://github.com/necolas/dotfiles/blob/master/bin/osxdefaults
[osxdefaults]: http://mths.be/osx

Issue: #12