v0.2.0

• Fix program version that is displayed when running oxipng -V
• Ensure --quiet mode is actually quiet (@SethDusek #20)
• Write status/debug information to stderr instead of stdout
• Use heuristics to determine best combination for -o1 (#21)
• [SEMVER_MAJOR] Allow 'safe', 'all', or comma-separated list as options for --strip
• [SEMVER_MINOR] Add -s alias for --strip