Init petrol cans (ensure age and name)

Added initialization of petrol can ages and names. Like chainsaws,
petrol can ages aren't saved, but the display names are. On game load I
can read the petrol can names and set the ages to the amount found in
the name.

Also added some debug code to work out what the Keyboard table looks
like.
Add description of Keyboard elements

I couldn't figure out what Keyboard was (in a short enough time) so I
just wrote a little util function to print out all the fields and
values in the Keyboard table.