This is because they may conflict with reserved names. Also took
this opportunity to make the guards in the zcash subdir a bit
more uniform by having them all conform to ZC_<...>_H_
This closes#1272
This is a new implementation of the incremental merkle tree used by our
scheme to witness commitments to spendable value. It serves as a fixed-sized
accumulator.
This new construction has a much simpler API surface area, avoids memory
safety issues, remains pruned at all times, avoids serialization edge cases,
has more efficient insertion, and is abstract over the depth and hash
function used at the type level.
Further, it lays the groundwork for efficient "fast-forwarding" of witnesses
into the tree as the treestate is updated.