hllSparseAdd() sanity check for span != 0 added.
hllSparseToDense API changed to take ref to object.

The new API takes directly the object doing everything needed to
turn it into a dense representation, including setting the new
representation as object->ptr.
PFDEBUG added, PFGETREG removed.

PFDEBUG will be the interface to do debugging tasks with a key
containing an HLL object.
PFDEBUG DECODE added.

Provides a human readable description of the opcodes composing a
run-length encoded HLL (sparse encoding).
The command is only useful for debugging / development tasks.
hllSparseToDense(): sanity check added.

The function checks if all the HLL_REGISTERS were processed during the
convertion from sparse to dense encoding, returning REDIS_OK or
REDIS_ERR to signal a corruption problem.

A bug in PFDEBUG GETREG was fixed: when the object is converted to the
dense representation we need to reassign the new pointer to the header
structure pointer.
hllSparseAdd(): more correct dense conversion conditional.

We want to promote if the total string size exceeds the resulting size
after the upgrade.
Fixed memmove() count in hllSparseAdd().