Initial dump for a boring-rustls-provider

This is just a dump of me figuring out how to interface with boring and rustls.
It works to establish a connection and exchange data but I haven't written real tests yet, nor did I cleanup the code or made the effort to make it look nice.
There is probably some code in here that should rather live in the `boring` crate.

Cargo.toml

@@ -0,0 +1,16 @@
+[workspace]
+members = [
+  # the main library and tests
+  "boring-rustls-provider",
+  # tests and example code
+  "examples",
+]
+default-members = [
+  "examples",
+  "boring-rustls-provider",
+]
+
+resolver = "2"
+
+[workspace.dependencies]
+rustls = { version = "=0.22.0-alpha.4", default-features = false }