Add completions to the dive location, buddy and divemaster entries

Add completions to the dive location, buddy and divemaster entries

This way you can just type the first few characters of a location you've
been to before, and it will show you a list of possible completions.
Same for buddies and divemasters (which take the completions from a list
of people you've used before).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>