Update API documentation to beta3 rc4

The PDF documentation is now a single PDF file generated with Sphinx.

The HTML documentation is now generated with Sphinx. The sole entry
point is index.html. modules.html no longer exists.
diff --git a/docs/html/_static/custom.css b/docs/html/_static/custom.css
new file mode 100644
index 0000000..2a924f1
--- /dev/null
+++ b/docs/html/_static/custom.css
@@ -0,0 +1 @@
+/* This file intentionally left blank. */