Support 15bpp color sixel. (-F option)
Replace indent tabs to spaces.
Remove a trailing space.
Add sixel_dither_unref() before return (-1).
Separate sixel_encode_impl() into sixel_encode_header(), sixel_encode_body() and
sixel_encode_footer().
Remove unnecessary check. (nwrite <= 0)
Merge branch 'arakiken' into arakiken-separate-sixel-encode-impl
Add pipe mode feature(-D/--pipe-mode)
Use fseek instead of rewind, and check the availability of fseek
Use clearerr instead of fseek
Merge branch 'hotfix-for-paletted-png' into feature-pipe-mode
Merge remote-tracking branch 'origin/develop' into arakiken

Conflicts:
	src/tosixel.c
Remove a performance hack which inserts '\n' after palette definition.
Update document for --pipe-mode
Include sys/select.h to fix build on MinGW environment
Minor fix
Include sys/types.h to use fd_set
Suppress GCC 4.9.1 warnings
Revert "Suppress GCC 4.9.1 warnings"

This reverts commit 289b2d7ec4f0e06fe5fc85a8b11eafe536331e04.
Amend fix for suppressing GCC warnings
Remove an extra space.