This just moves (and occasionally copies) blocks of text and/or
examples in preparation form more substantial streamlining.
No modifications were made to any block.

Make the Parameter, Encoding, and Header Object fixed fields
section organization the same in all three places, with the
same levels of indentation.

Add more headings under the Encoding Object for guidance on
each form media type, and sub-headings for each example in
each of those sections.

This will make the diff for the next commit much more legible.

This puts the useful part of the "An encoding attribute..."
text into the fixed fields table, and removes the duplication.

It also links the remaining stub or truncated sections to the
information's new location under the Encoding Object.

This re-organizes and streamlines the form-urlencoded guidance
that was consolidated from the Media Type Object.

It also adds an example of a base64-encoded URL query parameter.

I forgot to run the example through URL quoting, which is necessary.

This organizes and streamlines the guidance on multipart
that was incorporated from the Media Type Object.

Lots of duplication has been removed, and the examples
reworked to show distinct use cases.