Movie. Improve use of -F

[Esteban82]

From the slack group of 2021 Unavco Course:

Federico Esteban: Is it -F (in movie) mandatory? I use movie with -M and without -F and I get all the frames (and they would be deleted if I used -Z).
Paul Wessel: We may need to improve that. I would agree that if no -F and a -M then it should be the same as -Fnone -M

[PaulWessel]

Looking at this some more I remember that -Fnone is used to turn off the generation of the PNG frames. So right now we have this situation with -F:

mp4: Create the PNGs then assemble them into a MP4 movie
webm: Create the PNGs then assemble them into a webm movie
none: Do not create the PNGs
Default: Create the PNGs but do not make a movie.

Note -A can be used with -F to create both the full MPG and an (optionally shorter version via +s) GIF. Without -F we still produce the PNGs and hence -A work as well.

Users who do not wish to use FFmpeg to assemble the PNGs will want to create the PNGs and not the movies. That is a valid requist and currently the default. We could argue it if would have been better to have -Fpng to only create the PNGs rather than -Fnone to not create them. Perhaps it is worth making the change:

-Fpng|mp4|webm

If no -F then no frames unless -A is set (all frames) or -M (one frame). This would let use use -M without -Fnone. It would also force the user to select a product via -Fpng if that is what they want. I think this is a better system than what I implemented.

Thoughts, @GenericMappingTools/core ?

[PaulWessel]

Messy with -A and -M requiring certain settings in -F etc. I have decided to eliminate -A and merge it with -F in a more compact setup (backwards compatible of course):

-Fgif|mp4|webm|png[+l[n]][+oopts][+sstride][+t]

A PR will come after some testing.