* ADD new /src/common/crypto_rand.[ch] module.
* ADD new /src/common/crypto_util.[ch] module (contains the memwipe()
function, since all crypto_* modules need this).
* FIXES part of #24658: https://bugs.torproject.org/24658
We could use one of these for holding "junk" descriptors and
unparseable things -- but we'll _need_ it for having cached
consensuses and diffs between them.