Adding "alwaysinline" and "noinline" attributes to a function results in
an error similar to the following when compiling with LLVM:

```
Attributes 'noinline and alwaysinline' are incompatible!
LLVM ERROR: Broken module found, compilation aborted!
```

and then the interpreter is killed. This commit prevents both attributes
being added at the Python level, to prevent the above error message and
termination.

The `llvm:ref` directive seems to be unknown. I'm not sure how it did
work, but as this is used precisely once in the docs it seems reasonable
to just replace it with a URL.