* [Cleanup] Gender constants cleanup
# Notes
- Convert to a `Gender` namespace using `constexpr`.
- Cleanup spots where we were using magic numbers for gender values.
* Cleanup
# Perl
- Add `$npc->GetKeepsSoldItems()`.
- Add `$npc->SetKeepsSoldItems(keeps_sold_items)`.
# Lua
- Add `npc:GetKeepsSoldItems()`.
- Add `npc:SetKeepsSoldItems(keeps_sold_items)`.
# Notes
- Allows operators to keep specific NPCs from keeping items sold to them.
- Keeps NPCs from being cluttered with stuff like Cloth Caps, Bone Chips, etc.
1. Standard library functions snprintf & vsnprintf are available thusly named (without the prepended underscores). Someone may want to check my conditionals against non-MSVC compilers, though.
2. zone/bonuses.cpp throws an internal compiler error with optimize enabled; #pragma disable optimization on VS2015 only on function Mob::NegateSpellBonuses works around it.
