Apply @uobikiemukot's patch (various pixel-format support)
https://gist.github.com/uobikiemukot/7adab29310caf0be6f7a
Swap bytes if depth == 2
Keep compatibility
Merge pull request #8 from saitoha/fix-segfault-with-introducing-various-pixformat

Keep compatibility
@uobikiemukot's patch in the conversation of #8
Merge branch 'feature-support-various-pixformat' of github.com:saitoha/libsixel into feature-support-various-pixformat
Merge branch 'master' into feature-support-various-pixformat

Conflicts:
	converters/img2sixel.c
	include/sixel.h.in
	src/tosixel.c
Merge branch 'hotfix-preventing-double-free' into feature-support-various-pixformat
Merge branch 'master' into release-1.3
Merge branch 'develop' into release-1.3
Update version
Update ChangeLog
Add pipe mode feature(-D/--pipe-mode)
Use fseek instead of rewind, and check the availability of fseek
Use clearerr instead of fseek
Interpret an image expanded by png_set_palette_to_rgb as a 3-channel image
Merge branch 'hotfix-for-paletted-png' into feature-pipe-mode
Merge branch 'develop' into release-1.3
Merge branch 'hotfix-for-paletted-png' into release-1.3
Bump version