Automatically document all rust crates

Additionally, add a ./dev_tools/cargo-doc.sh script that builds and
opens the documentation for any documented rust target.

Change-Id: I2a52adaf90ca93cb749415260c02f3777a53ddf6
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/BUILD b/aos/BUILD
index a887edc..d9781f9 100644
--- a/aos/BUILD
+++ b/aos/BUILD
@@ -225,6 +225,7 @@
     testonly = True,
     srcs = ["test_init.rs"],
     crate_name = "aos_test_init",
+    docs = False,
     libs = [
         "//aos/testing:tmpdir",
     ],