doc: fix formatting in tty.markdown

Fixes #5135.
doc: child_process: document 'error' event

Fixes #5130.
openssl: disable HEARTBEAT TLS extension

Microsoft's IIS doesn't support it, and is not replying with ServerHello
after receiving ClientHello which contains it.

The good way might be allowing to opt-out this at runtime from
javascript-land, but unfortunately OpenSSL doesn't support it right now.

see #5119