Split Section 6 into Header + Content

[edadesd]

Section 6 seemed awkward with the content all formatted on the same level as other headers, so I broke it up into a header and content. Issue #22 mentioned this as something to fix.

To give it an effect instead of just reciting facts, I phrased it as a reservation of rights in non-US countries where the work may be entitled to copyright. I think this still conveys the basic understanding that the work is not subject to copyright in the US but may be subject to copyright elsewhere.

There were some wording edits to Sections 1 and 4 intended to improve clarity.

In Section 2, I used "becomes" instead of an equals sign to indicate transformation rather than logical equivalence.

[tomberek]

Looks good to me.

Note: if we merge, I'll do a squash.

[tomberek]

Subsumes #49

[BrandonBouier]

changes made, @edadesd. Thanks for your contribution!