Add input parameter validation for some functions
Add NULL checks
Add NULL checks
Bump version
Introduce new APIs: sixel_output_{get,set}_skip_dcs_envelope
Merge branch 'develop' into arakiken
Apply arakiken's patch for GNU Screen integration:
http://mlterm.sourceforge.net/libsixel-penetrate.patch
Fix build broken by fb1cd8a
Introduce -C(complexion score) option and implement complexion correction
Merge arakiken's amend patch:
http://mlterm.sourceforge.net/libsixel-penetrate2.patch
Merge branch 'develop' into sandbox
Update libtool minor version
Merge branch 'master' into release-1.2

Conflicts:
	configure
	configure.ac
	package.json
Merge branch 'feature-screen-penetration' into release-1.2
Skip an unknown code(0x3c) at GIF decoder
Merge branch 'hotfix-for-corrupted-gif' into release-1.2
Merge branch 'feature-customize-dcs-envelope' into release-1.2

Conflicts:
	configure
	configure.ac
	include/sixel.h.in
	src/tosixel.c
Merge branch 'hotfix-for-corrupted-gif' into release-1.1
Bump version
Merge branch 'fix-issue-5' into release-1.2

Conflicts:
	src/output.c