The attached patch makes it so that 'code object' is its own 'top-level' entry in the index instead of being 'code' with an 'object' sub-item.  It also makes the links from the index go to the location in the documents just before the header instead of having the header be off-screen when the user navigates to it.

One thing about the ordering of the generated links, though, is that sphinx appears to generate them based on the alphabetical ordering of the path to the files that they're in:

c-api/code.rst
library/marshal.rst
library/stdtypes.rst
reference/datamodel.rst

If the order is that important, I believe it would require us to create sub-items that could look like this:

code object
    C API
    built-in type
    type reference
    marshaling

It didn't seem like other indexed entries follow this breakout pattern, but if that's what's desired for this case, just let me know and I'll submit a different patch.