CLI_ABI: smaller markdown subheadings
CLI_ABI: smaller markdown subheadings

The old ones were rendered by github almost as big as the parent headings.
davesteele/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs