v3.0.2: Fix homebrew issue and some improvements

Changes since v3.0.1

• tests/apk: Add tests (Credit: @mondeja)
• lib/*: All POSIX, except lib/cave
• lib/homebrew: Fix shell switching issue (Fixes #170)
  that makes the program broken since v3.0.0
• lib/dpkg/{Qc,Qe}: Add (Credit: @mondeja)
• lib/zypper: POSIX ready, tests added, minor fixes
• lib/zypper/Sg: Add (Credit: @mondeja)
• lib/zypper/Sii: Removed as it's too slow.
• Improve the way the program deals with back-end's
  optional arguments (Fixes #173)

Deprecation

• lib/homebrew/Rs: temporarily deprecated
• lib/homebrew/Qo: temporarily deprecated

Development

• tests/ can run in parallel
• tests can support any custom Dockerfile