Stop the documentation buffer from jumping around

[gabc]

Instead of always creating a new buffer. Just use the old one if it's there (create if not).

So that if I place the documentation buffer at one place, it doesn't get moved around when I request the documentation of another operator.

[lokedhs]

Thank you. Merged with a small simplification. Please check to see if it still works as expected.

[gabc]

Yes it works, thanks for the simplification I wasn't aware of it. Thank you.