* crypto/merkle: Remove byter in favor of plain byte slices
This PR is fully backwards compatible in terms of function output!
(The Go API differs though) The only test case changes was to refactor
it to be table driven.
* Update godocs per review comments
Currently the top level directory contains basically all of the code
for the crypto package. This PR moves the crypto code into submodules
in a similar manner to what `golang/x/crypto` does. This improves code
organization.
Ref discussion: https://github.com/tendermint/tendermint/pull/1966Closes#1956