How to update a Data Extension in ExactTarget with PHP

ExactTarget's documentation leaves something to be desired... It took me a while to figure this out, and it came mostly out of trial and error or other users like me who posted tutorials. So I wanted to pay it forward by posting my experience here, in hopes that it will help someone. The tutorial is below, but the entire directory is also available in my downloads section, at the bottom of this page, or in my github repository.

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