502 map bin keys

[dburyak]

Implements #502 . Adds support for binary keys in MultiType. Specifically, this is needed for reading binary fields (keys) of HASH-es with HGETALL command.

The approach is to always store elements of multi in multi array, and evaluate corresponding map with string or/and binary keys when either is requested. This approach makes this class NOT thread safe, but it is not a really useful feature since under typical usage scenarios there won't be concurrent access. Hence, it's better to keep this class simple and not-thread-safe, and if the need to use it concurrently arises in some exotic use cases, then let the callers deal with it externally.

NOTE: I had to decide whether to keep using un-ordered HashMap for binary keys too, or change both strMap and binMap to be LinkedHashMap. In fact, Redis preserves order of fields in HASH-es, and relevant commands like HKEYS, HVALS, HSCAN and HGETALL particularly, return values in their respective order. With this change, the existing method MultiType#getKeys() will also preserve order, which was not the case due to usage of HashMap. Even though technically this is a change of behavior, it can not affect any existing users, as they were unable to rely on the order anyway prior to this change.