Show only first frame of animated webp

Minor typo from 1.8.1. Compared to 1.8.0, now handles animated webp format same as gif (just first frame).

Handle animated webp same as gif

Only show first frame if no filenames were specified on the command line.

Fix scrolling for genuine VT340, foot, and other terminals

After purchasing a genuine DEC VT340 terminal, @hackerb9 has learned that the DEC VT340 graphics programmer's manual was mistaken and the sense of DECSDM should be inverted. Nearly every terminal emulator which built upon that reference over the last thirty years is incorrect. Some are correcting the error now, some never were wrong, but we are at a time when it is not safe to presume what setting DECSDM means.

For now, lsix will simply presume that sixel scrolling is enabled and hope that no program has been run before it that disables it.

See #41 for details.

Thanks go to @j4james for pointing out the mistake and for testing multiple terminal emulators to show that none of them currently default to having sixel scrolling disabled.

Bug fix for spaces in filenames

The last release added a regression such that files specified on the command line could not have spaces. All good now.

Directories & webp

Add support for viewing directories specified on the command line. Also, webp is shown by default now. Other minor fixes like dash at the beginning of a filename and checking the LSIX_FORCE_SIXEL_SUPPORT variable.

MacOS support

Various patches, including the ones that helped with MacOS support.

Sixel detection

Now detects if the terminal cannot handle SIXEL and exits with an error.

Initial release

All the basics working release.