Pull in latest BearSSL head (0.6 + minor additions) release and add AES_CCM
modes to the encryption options. Enable the aes_ccm initialization in client/server
The EC mul20 and square20 code was identical in two different files,
but because these copies were static, we ended up with an extra 6k of
duplicated code. Updated BearSSL to make them shared, saving 6KB.
