Update .travis.yml
Merge branch 'master' into travis
Issue #5: Completion of error handling
Merge branch 'fix-issue-5' into release-1.1
Update version
Fix for some environment missing "getopt_long"
Merge remote-tracking branch 'origin/hotfix-for-env-missing-getopt_long' into release-1.1
Fix Issue #6: Remove unnecessary null pointer checks
Merge branch 'fix-issue-6' into release-1.1

Conflicts:
	converters/img2sixel.c
Fix a regression bug introduced by 0221665
Merge branch 'fix-issue-6' into release-1.1
Merge branch 'develop' into release-1.1
Fix a compile error
Fix a compile error
Merge branch 'fix-issue-6' into release-1.1
Merge branch 'release-1.1'
Add input parameter validation for some functions
Add NULL checks
Add NULL checks
Bump version