- add COMMAND GETKEYSANDFLAGS sub-command
- add RM_KeyAtPosWithFlags and GetCommandKeysWithFlags
- RM_KeyAtPos and RM_CreateCommand set flags requiring full access for keys
- RM_CreateCommand set VARIABLE_FLAGS
- expose `variable_flags` flag in COMMAND INFO key-specs
- getKeysFromCommandWithSpecs prefers key-specs over getkeys-api
- add tests for all of these
This cleans up and simplifies the API by passing the command name as the
first argument. Previously the command name was specified explicitly,
but was still included in the argv.
This is essentially the same as calling COMMAND GETKEYS but provides a
more efficient interface that can be used in every context (i.e. not a
Redis command).
