Version 0.5.1 RELEASED.
Started reworking the mmap driver.
More work in the new mmap driver.
borotool no longer can assume sizes % 64 because of filler blocks.
Call boro_node_d() in boro_unref().
Reverted boro_set_left() and boro_set_right().

Because boro_node_d() was not being called in all cases.
The key strdup() + free() in clone_node() is no longer needed.
Got rid of clone_node().
Changed boro_set_left() and boro_set_right() to use a boro_node.