Location awareness and new API exposure depending on version.

• Added pkcs header.
• Renamed repo to back to OpenSSL. Broke too many things.
• Added rsa header.
• Added shim to make it easier to use regardless of location and add new inline APIs to exposed functionality in newer versions of OpenSSL. PR #3
• Added new inline function to shim to allow setting to AUTO ECDH mode when linking with OpenSSL v1.0.2 or higher up to OpenSSL v1.1.0 where the function becomes a no-op because this mode is set automatically.
• Swift 4 support.