Update Fun module (#421)

* Fun: Replace ENTINDEX with TypeConversion for consistency

* Fun: Add a class wrapping player's data

* Fun: Make TraceLine a post forward

Reason: as it is it breaks plugins hooking TraceLine because of the original game call is being superceded and other modules can't catch it. It looks like it's this way from the very start fun module has been introduced 13 years ago before. Fakemeta module comes a little later.

* Fun: Clean up code

* Fun: Toggle PlayerPreThink forward on demand

* Fun: Toggle TraceLine forward on demand

* Fun: Add HITZONE* constants for use with set/get_user_hitzone()

* Fun: Refactor a litte the player class

* Fun: Clean up a little more

* Fun: Fix typo in set_user_hitzones from previous commit

plugins/include/fun.inc

@@ -21,6 +21,21 @@
 	#pragma loadlib fun
 #endif
 
+
+/**
+ * Parts of body for hits, for use with set_user_hitzones().
+ */
+const HITZONE_GENERIC  = (1 << HIT_GENERIC);   // 1
+const HITZONE_HEAD     = (1 << HIT_HEAD);      // 2
+const HITZONE_CHEST    = (1 << HIT_CHEST);     // 4
+const HITZONE_STOMATCH = (1 << HIT_STOMATCH);  // 8
+const HITZONE_LEFTARM  = (1 << HIT_LEFTARM);   // 16
+const HITZONE_RIGHTARM = (1 << HIT_RIGHTARM);  // 32
+const HITZONE_LEFTLEG  = (1 << HIT_LEFTLEG);   // 64
+const HITZONE_RIGHTLEG = (1 << HIT_RIGHTLEG);  // 128
+const HITZONES_DEFAULT = HITZONE_GENERIC | HITZONE_HEAD     | HITZONE_CHEST   | HITZONE_STOMATCH | 
+                         HITZONE_LEFTARM | HITZONE_RIGHTARM | HITZONE_LEFTLEG | HITZONE_RIGHTLEG; // 255
+
 /**
  * Tells whether receiver hears sender via voice communication.
  *
@@ -169,26 +184,18 @@ native give_item(index, const item[]);
  *
  * @param index         Client index
  * @param target        The target player
- * @param body          A bitsum of the body parts that can/can't be shot:
- *                      1   - generic
- *                      2   - head
- *                      4   - chest
- *                      8   - stomach
- *                      16  - left arm
- *                      32  - right arm
- *                      64  - left leg
- *                      128 - right leg
+ * @param body          A bitsum of the body parts that can/can't be shot. See HITZONE* constants.
  *
  * @noreturn
  * @error               If player is not connected or not within the range
  *                      of 1 to MaxClients.
  */
-native set_user_hitzones(index = 0, target = 0, body = 255);
+native set_user_hitzones(index = 0, target = 0, body = HITZONES_DEFAULT);
 
 /**
  * Gets the set of hit zone "rules" between @index and @target players.
  *
- * @note For the body part bitsum take a look at the set_user_hitzones() native.
+ * @note For the body part bitsum, see HITZONE* constants.
  *
  * @param index         Client index
  * @param target        The target player