fixes and improvements

• add support for lzip archives (#4 (closed))
• add support for gitsm fetcher (#5 (closed))
• add support for SRC_DOWNLOAD_URL (#6 (closed))
• add support for recipes with unpinned versions (#7 (closed))
• handle cases where CVE data are absent (#8 (closed))
• use "git archive" for deterministic output when packaging git repos (#10 (closed))
• correctly handle temp dirs (#11 (closed))
• add option for custom temp dir (#12 (closed))