Create proto format flag on Stardoc to output raw form of protos. (#191)

stardoc/stardoc.bzl

diff --git a/stardoc/stardoc.bzl b/stardoc/stardoc.bzl
index b1bba05..f22ac89 100644
--- a/stardoc/stardoc.bzl
+++ b/stardoc/stardoc.bzl
@@ -34,6 +34,7 @@
     args.add("--input=" + str(ctx.file.input.owner))
     args.add("--output=" + ctx.outputs.out.path)
     args.add("--workspace_name=" + ctx.workspace_name)
+    args.add("--output_format=" + ctx.attr.format)
     args.add_all(
         ctx.attr.symbol_names,
         format_each = "--symbols=%s",
@@ -82,6 +83,11 @@
             doc = "A list of skylark_library dependencies which the input depends on.",
             providers = [StarlarkLibraryInfo],
         ),
+        "format": attr.string(
+            doc = "The format of the output file.",
+            default = "markdown",
+            values = ["markdown", "proto"],
+        ),
         "out": attr.output(
             doc = "The (markdown) file to which documentation will be output.",
             mandatory = True,

test/self_doc_golden.md

diff --git a/test/self_doc_golden.md b/test/self_doc_golden.md
index a6492f9..dae7e1f 100755
--- a/test/self_doc_golden.md
+++ b/test/self_doc_golden.md
@@ -5,7 +5,7 @@
 ## stardoc
 
 <pre>
-stardoc(<a href="#stardoc-name">name</a>, <a href="#stardoc-deps">deps</a>, <a href="#stardoc-input">input</a>, <a href="#stardoc-out">out</a>, <a href="#stardoc-semantic_flags">semantic_flags</a>, <a href="#stardoc-stardoc">stardoc</a>, <a href="#stardoc-symbol_names">symbol_names</a>)
+stardoc(<a href="#stardoc-name">name</a>, <a href="#stardoc-deps">deps</a>, <a href="#stardoc-format">format</a>, <a href="#stardoc-input">input</a>, <a href="#stardoc-out">out</a>, <a href="#stardoc-semantic_flags">semantic_flags</a>, <a href="#stardoc-stardoc">stardoc</a>, <a href="#stardoc-symbol_names">symbol_names</a>)
 </pre>
 
 
@@ -40,6 +40,15 @@
         </p>
       </td>
     </tr>
+    <tr id="stardoc-format">
+      <td><code>format</code></td>
+      <td>
+        String; optional
+        <p>
+          The format of the output file.
+        </p>
+      </td>
+    </tr>
     <tr id="stardoc-input">
       <td><code>input</code></td>
       <td>