Door NFRC values

[shorowit]

Closes #279.

1. Adds UFactor and SHGC elements for doors.
2. Adds DoorDescription element. Choices based on NFRC are: "embossed", "flush", "full lite", "1/2 - lite", "1/4 - lite", "3/4 - lite", "raised panel", and "other".
3. Clarifies that UFactor/RValue elements (for doors, windows, and skylights) include air films.

Should we mark RValue as deprecated, so that UFactor is used instead going forward?

[shorowit]

Copy over other elements like Overhangs (or use WindowInfo group of elements).
Note that the WindowType proposal allows a door choice.
Some support for marking RValue as deprecated.

[shorowit]

It would be hard to further improve this without making breaking changes. I suggest we defer this until v4.0 and do this correctly.

[nmerket]

Discussion in 7/21/2021 Working Group Meeting