APIs added for these stream operations: add, delete, iterate and
trim (by ID or maxlength). The functions are prefixed by RM_Stream.
* RM_StreamAdd
* RM_StreamDelete
* RM_StreamIteratorStart
* RM_StreamIteratorStop
* RM_StreamIteratorNextID
* RM_StreamIteratorNextField
* RM_StreamIteratorDelete
* RM_StreamTrimByLength
* RM_StreamTrimByID
The type RedisModuleStreamID is added and functions for converting
from and to RedisModuleString.
* RM_CreateStringFromStreamID
* RM_StringToStreamID
Whenever the stream functions return REDISMODULE_ERR, errno is set to
provide additional error information.
Refactoring: The zset iterator fields in the RedisModuleKey struct
are wrapped in a union, to allow the same space to be used for type-
specific info for streams and allow future use for other key types.
