Add a turn number to the calendar object because it's accessed so much.
Merge pull request #7620 from kevingranade/turn-number

Add a turn number to the calendar object because it's accessed so much.
Fix inventory_ui bug where worn items would not get dropped:

because the check for is_null must be inverted, dropping the item when it is not null.
And the iteration should start at worn.size()-1 and go backwards, as worn.size() will change during this iteration.
remove ? as a possible item hotkey in inventory
Merge pull request #7624 from cdepatie/hotkey_conflict_fix

remove ? as a possible item hotkey in inventory
Enable c++11 compilation and use a few of the features.
Fix .cbp syntax.
Convert options table to an unordered map.