Merge pull request
#3756 from minrk/wiredoc
document the wire protocol
in the messaging doc
also update the digest scheme to use sha256 and make this configurable,
since md5 is the previous default and has been shown to be bad.
More messaging docs to update here:
- [x] remove get/setattr on kernel
- [x] remove crash messages
- [x] completion requests do not behave as documented
- [x] object_info is misdocumented (`name` is actually `oname` in object_info_request)