Use rules_pkg for building releases

This commit allows the creation of distributions, with 0.0.1 being the first version.
See distro/README.md for details on how to build a release.

This commit also uses a new version of the Bazel federation that contains rules_pkg 0.2.2 instead of 0.2.1.

There are still some problems with the WORKSPACE stanza that is being printed by the release notes generation script, though:
- It references a //cc:deps.bzl file, which doesn't exist. I have to modify the scripts in rules_pkg to support a flag like 'has_deps'.
- It doesn't support the Bazel federation yet, since it always tells users to download code from the rules_cc repository.

cc/BUILD

diff --git a/cc/BUILD b/cc/BUILD
index 333a58a..21ee541 100644
--- a/cc/BUILD
+++ b/cc/BUILD
@@ -44,3 +44,14 @@
     ],
     visibility = ["//visibility:public"],
 )
+
+# TODO(aiuto): Find a way to strip this rule from the distribution tarball.
+filegroup(
+    name = "distribution",
+    srcs = glob([
+        "**",
+    ]),
+    visibility = [
+        "//distro:__pkg__",
+    ],
+)