`--dry-run` and "gzip-suffix" strategy

• #4 --dry-run option for peace of mind, any of the following are equivalent

  cdn-sync --dry-run go
  cdn-sync -n go
  cdn-sync go --dry-run
  cdn-sync go -n
  

  These will run all checks and compare local files with remote files, but no changes will be made.

• new "gzip-suffix" strategy

  • "strategy": ["gzip-suffix"]: files are GZIP deflated and .gz is appended to their filenames, probably not particularly useful by itself
  • "strategy": ["clone", "gzip-suffix"]: as above, but the original (uncompressed) versions are also uploaded, so a single CDN can host both GZIP deflated files and uncompressed files