bazel: genasciidoc and genasciidoc_zip rule

Implement genasciidoc rule for bazel. It's a filegroup containing all
the html and resource files.

Also implement genasciidoc_zip rule for bazel, which is similar to
buck's genasciidoc rule to produce a zip file containing all asciidoctor
generated and resource files.

TEST PLAN:
  bazel build Documentation
  buck build Documentation:html
  diff -u bazel-bin/Documentation/install.html buck-out/gen/Documentation/html__tmp/Documentation/install.html

Change-Id: I3065355800a982c6956d3bb634204baaa60c045e

gerrit-prettify/BUILD

diff --git a/gerrit-prettify/BUILD b/gerrit-prettify/BUILD
index 063feee..b8d4dd6 100644
--- a/gerrit-prettify/BUILD
+++ b/gerrit-prettify/BUILD
@@ -33,3 +33,8 @@
   ],
   visibility = ['//visibility:public'],
 )
+
+exports_files([
+  'src/main/resources/com/google/gerrit/prettify/client/prettify.css',
+  'src/main/resources/com/google/gerrit/prettify/client/prettify.js',
+])