Added the TSPlayer.Hostile property.

It gets `TPlayer.hostile`.
I also wanted to add the ability to change `TPlayer.hostile`, but noticed a property `TSPlayer.Team`. You can only use the `TSPlayer.SetTeam` method to change it. So it's exactly the same here: You can use the method `TSPlayer.SetPvP` (By the way, it should be renamed to `TSPlayer.SetHostile`)

TShockAPI/TSPlayer.cs

@@ -1147,6 +1147,11 @@ namespace TShockAPI
 			get { return TPlayer.team; }
 		}
 
+		/// <summary>
+		/// Gets PvP player mode.
+		/// </summary>
+		public bool Hostile => TPlayer.hostile;
+
 		/// <summary>
 		/// Gets the player's X coordinate.
 		/// </summary>