documentation: make it possible to have more than 128 results for a node.

documentation: make it possible to have more than 128 results for a node.

Python's __init__ is the main offender, the (currently very barebone)
Magnum Python bindings have 340 results for __init__. This change is
based on the assumption that nodes with extreme amount of results on the
other hand don't have many children, so we can steal some bits from the
child count instead. Now it's either up to 127 results and up to 127
children or up to 2048 results and 16 children.