init

This builds a very basic version of the nats.c client (no TLS, no
streaming/jetstream/whatever, since those bring in complex
dependencies and I do not need them at the moment). Right now it
contains a simple test program that demonstrates the functionality
(cool!), but the plan is for the nats.zig to bind the API into a
nicer, zig-like shape and re-export it. Then this becomes a package.
The current function could become a test, though it's a bit complex
for a unit test (and requires connecting to an externally-running NATS
server in order to work).

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "deps/nats.c"]
+	path = deps/nats.c
+	url = https://github.com/nats-io/nats.c.git