Add PDF 1.6 Spec Text (or Note) Annotation.

[mayanez]

This add the "Text" annotation as referred to by the PDF spec. These are the "Pop-up" style annotations typically used for comments.

I'm unsure about what the proper changes are for testing so let me know if it needs modification.

[mjbryant]

This looks great! Thanks for the contribution. If you uncomment the integration test lines you added and check the file after the tests have run we can merge it in.