Fix documentation generation on Windows.

Previously doc/doc.css was a symlink to util/doc.css, but symlinks
don't work well on Windows. Now util/doc.css is copied to the output
directory when the documentation is generated.

Change-Id: I2c9f4fee4f4307cc3dd70c4be380b4551d5e9ab5
Reviewed-by: David Benjamin <>
Reviewed-by: Adam Langley <>
diff --git a/.gitignore b/.gitignore
index b54125f..a2e3ed2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@