Enhanced check for auto-wielding

Consider martial art style and unarmed combat compatibility for
auto-wielding.

Rewrite player::get_combat_style to be much simpler (and const).

Force invlet to new wielded item on pickup, also display a message
when the pickup leads to wielding an item (already done in some
cases but not in all).

Made some functions const as needed.
Removed unused variable ma_styles, is now part of the player class.