Adds filters (--tag, --pattern, --expired-only) to filter the keys - #10

Summary

Adds --tag, --pattern, --expired-only filtering to the keyscommand for filtering out the list of keys.

Notes

• Uses fnamtch for pattern matching with --pattern command for glob-style matching against keys names.
• Added handle_timeout decorator to the cmd_key as now it uses cache.get() which can throw Timeout error.
• --tag and --expired-only needs the metadata for the keys. That is fetched for them.
• Multiple filters can be combined with AND logic.

Testing

• Adds 11 new tests, all passes successfully with the existing ones. Test coverage is at 98.37%