Clarications on RFC6570-derived behavior (3.2.0 port of 3818)

This aligns allowReserved with style by similarly correlating it
with RFC6570 operators.  This will make it easier to write a more
in-depth explanation of the process in an appendix.

This also adds one of several appendixes to be added to clarify
the most obscure details of Parameter Object and Encoding Object
serialization.

This clarifies the correspondence between OAS fields and RFC6570
operators, and acknowledges that some field values and combinations
do not have analogues.  It provides further guidance for how to
use RFC6570 implementations to support these configurations.

This includes a SHOULD directive regarding using RFC6570 expansion
with the non-RFC6570 styles, as the use of "explode" and
"allowReserved" does not otherwise make any sense.  It perhaps
could be a MUST.

Examples are included to show both typical usage, and how to
work around the lack of exact RFC6570 equivalences for certain
configurations.