Create a folder if it doesn't already exist

I've run into a few cases with WordPress installs with [Bluehost][1] where I've encountered errors with my WordPress theme because the uploads folder `wp-content/uploads` was not present. Apparently the Bluehost [cPanel][2] WordPress installer does not create this folder, though [HostGator][3] does. So I need to add code to my theme that checks for the folder and creates it otherwise. [1]: https://en.wikipedia.org/wiki/Bluehost [2]: https://en.wikipedia.org/wiki/CPanel [3]: https://en.wikipedia.org/wiki/HostGator