A bit hacky, since CLForm can't seem to initialize properly without
being part of a request. To avoid a reference-before-assignment error,
the INDEX variable is first initialized as a global in __init__.py. But
it is definitely faster. Repeated renders take around 2ms each. Reading
the cached value takes about 0.002ms.
Also split index() into index_get() and index_post(), since GET calls
always use the cached version, and POST calls never do.