Some doc fixes (#100)

* fix up Args doc block.

* add a module doc string

rules/build_test.bzl

@@ -39,7 +39,7 @@ def build_test(name, targets, **kwargs):
     Args:
       name: The name of the test rule.
       targets: A list of targets to ensure build.
-      kwargs: The <a href="https://docs.bazel.build/versions/master/be/common-definitions.html#common-attributes-tests">common attributes for tests</a>.
+      **kwargs: The <a href="https://docs.bazel.build/versions/master/be/common-definitions.html#common-attributes-tests">common attributes for tests</a>.
     """
     if len(targets) == 0:
         fail("targets must be non-empty", "targets")

tests/build_test_tests.bzl

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+"""Unit tests for build_test.bzl."""
+
 load("//rules:build_test.bzl", "build_test")
 
 def build_test_test_suite():