Display yearly/monthly statistics

Display yearly statistics in a statistics window with option to expand
the viewing on monthly level. The amount of dives along with basic
information like duration, depth, water temperature and air consumption
is displayed in yearly and monthly level. Thus you are able to compare
e.g. development of air consumption or diving activity from year to
year.

Using already existing macro for splitting seconds into minutes:seconds.
Moving repetitive code to a function (couldn't think of the suggested
clever macro, but this should pretty much do the trick).
Now the statistics are updated every time the process_all_dives function
is called. It might make sense to actually verify the structures need to
be re-allocated, but such optimization is currently not implemented.

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>

Combined two commits.
Minor cleanups for white space and boolean values.
Significant changes to use the correct units for volumes vs. depths and to
avoid unneccesary lookups of the model storage based on the tree.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

save-xml.c

@@ -7,8 +7,6 @@
 
 #include "dive.h"
 
-#define FRACTION(n,x) ((unsigned)(n)/(x)),((unsigned)(n)%(x))
-
 static void show_milli(FILE *f, const char *pre, int value, const char *unit, const char *post)
 {
 	int i;