Add a dummy TLS implementation to be used as fallback

---
Added some more exports used by the server example

Includes-commit: d7be54b
Includes-commit: e36e6e7
Replicated-from: cloudflare#277

Author: palant

.bleep

@@ -1 +1 @@
-4c2c0ae61a505ccb25a0b39a5ca081d02fd64ba2
+b01a9bc71ff892b2fdbb47f6bb3f9eac88907435

pingora-core/src/lib.rs

@@ -58,6 +58,9 @@ pub use pingora_boringssl as tls;
 #[cfg(all(not(feature = "boringssl"), feature = "openssl"))]
 pub use pingora_openssl as tls;
 
+#[cfg(all(not(feature = "boringssl"), not(feature = "openssl")))]
+pub mod tls;
+
 pub mod prelude {
     pub use crate::server::configuration::Opt;
     pub use crate::server::Server;