The old code was wild: For the yearly statistics it would allocate
one entry per dive in the log. Of course, it would also leak
C-style strings.
Convert the whole thing to somewhat idiomatic C++.
Somewhat wasted work, because I'd like to convert the whole thing
to the new statistics code. But let's finish the conversion to C++
first.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
