ra-tls intends to establish the link between hardware-based remote
attestation and TLS secure channel implementation, which provides
more flexibilities on enclave management and communication.

This is the initial PoC implementation, and the code base of current
implementation is mainly inspired from
https://github.com/cloud-security-research/sgx-ra-tls.
Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>