changes to notcurses 2.1.6

[Nick Black]

All Notcurses users and packagers are encouraged to look over
issue #339 and the PR I'll be putting up later today:

https://github.com/dankamongmen/notcurses/issues/339

From the very beginning, I've worried about the large dependency
chain introduced by FFMpeg/OpenImageIO. With this change, it
ought be possible to install Notcurses through one's package
manager and get a minimal version; more importantly,
applications can depend on notcurses-core, and only require that
minimal version.

If you don't mind the multimedia stack (or need it), you
continue to use `pkg-config notcurses` as before. If you want
the minimal stack only, use `pkg-config notcurses-core`. By this
arrangement, the intuitive path leads to full capabilities,
hopefully minimizing the kind of bug reports that come from
people who don't bother to read one's documentation.

Unless/until C++/Python/Rust reflect this split, they're built
against the full Notcurses. Wrapper maintainers can choose
whether or not they want to reflect this granularity.

This change will be present in 2.1.6. Like I said, there are no
changes necessary for existing code, but those not using
multimedia can strip back their linkage.

Note that `notcurses_canopen_images()` and
`notcurses_canopen_videos()` continue to correctly work, and all
symbols are present, so it's possible to write apps that compile
without #ifdefs etc. against either form of the library, and
have their behavior decided at run- (well, link-)time.

hack on!

--rigorously, nick

--
nick black -=- https://www.nick-black.com
to make an apple pie from scratch,
you need first invent a universe.