Add support for SSL renegotiation

Implement support for initiating renegotiation as well as support for responding to a renegotiation request from client or server sides.

Potential implementation questions:

• should the mode change during renegotation?
• should a renegotiation request be automatically processed or should the application be notified of the renegotiation request and have the ability to choose to not renegotiate or continue with renegotiation>
• any concurrency issues (initiating a read or write from another thread when renegotiation is initiated)?