#17 option to save to a zipped file format

[Mj Mendoza IV]

internal testing shows 48frames with fair enough drawings already saves 1MB KSF file, while XML format is true to being open, filesize may soon be a problem -- manually zipping with 7zip's normal ZIP compression level brings it down to 22KB.

NOTE: as forward compatibility, supporting images may require including image file inside zipped file format

[Mj Mendoza IV]

some options

• https://www.libarchive.org/ -- BSDL; C lib
• https://github.com/rikyoz/bit7z -- MPL; C++ lib