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
14fdf9342e