Markdown: add minimal support for AST to HTML

Includes extension support to walk the AST and produce a table
of contents from the contained HeaderNodes.

Rendered HTML is blessed as SanitizedContent for Soy to include
inside of templates without further escaping.

Change-Id: Ib53e091617b39e22a230da9ec8a4aa39c3bf5c26

lib/ow2/BUCK

diff --git a/lib/ow2/BUCK b/lib/ow2/BUCK
new file mode 100644
index 0000000..c4339ce
--- /dev/null
+++ b/lib/ow2/BUCK
@@ -0,0 +1,29 @@
+VERSION = '5.0.3'
+
+maven_jar(
+  name = 'ow2-asm',
+  id = 'org.ow2.asm:asm:' + VERSION,
+  sha1 = 'dcc2193db20e19e1feca8b1240dbbc4e190824fa',
+  license = 'ow2',
+)
+
+maven_jar(
+  name = 'ow2-asm-analysis',
+  id = 'org.ow2.asm:asm-analysis:' + VERSION,
+  sha1 = 'c7126aded0e8e13fed5f913559a0dd7b770a10f3',
+  license = 'ow2',
+)
+
+maven_jar(
+  name = 'ow2-asm-tree',
+  id = 'org.ow2.asm:asm-tree:' + VERSION,
+  sha1 = '287749b48ba7162fb67c93a026d690b29f410bed',
+  license = 'ow2',
+)
+
+maven_jar(
+  name = 'ow2-asm-util',
+  id = 'org.ow2.asm:asm-util:' + VERSION,
+  sha1 = '1512e5571325854b05fb1efce1db75fcced54389',
+  license = 'ow2',
+)