Add Magnesium streaming format

Current Neon-SR2 streaming format has a few deficiencies:

1. it encodes MapEntry key values twice, once in the leaf itself and once in the entry's NodeIdentifierWithPredicates
2. it is 'zero-happy', i.e. they do not recognize that integer codes and sizes are typically much smaller than the 4-byte range and thus much of the stream is just small ints encoded as 4 bytes
3. while they are simple and straighforward, they also end up wasting bits – the four token families (codes, value types, node types, path argument types) each have at most 15 distinct values, and hence the bytes used to transmit them have 4 empty bits (or more)

Furthermore it cannot deal with Uint8/16/32/64 types, which is a must for the MRI window.