store bookkeeping in a map; save to XML

show total coins in bookkeeping
don't wipe out old bookkeeping data, so "total" doesn't become
meaningless after a year of data (or after the date has been changed
a couple times)
the XML is ~2megs for four years of data and takes about a second to
save on my system (reasonable enough)

stepmania/src/ScreenBookkeeping.cpp

@@ -145,6 +145,9 @@ void ScreenBookkeeping::ChangeView( View newView )
 			float fAverage = iTotalLast/(float)NUM_LAST_DAYS;
 			sData += ssprintf("%.1f\n",fAverage);
 			
+			sTitle += "Grand Total\n";
+			sData += ssprintf( "%i\n", BOOKKEEPER->GetCoinsTotal() );
+
 			m_textCols[0].SetHorizAlign( Actor::align_left );
 			m_textCols[0].SetText( sTitle );
 			m_textCols[1].SetText( "" );