Adds new type of wounds - piercing.

Unlike cuts they do not merge, so many small-damage stabs will create many small stab wounds instead of one megahole.
Also cleans up checks in wound code a bit with power of OOP

code/__defines/damage_organs.dm

@@ -9,6 +9,7 @@
 
 #define CUT       "cut"
 #define BRUISE    "bruise"
+#define PIERCE    "pierce"
 
 #define STUN      "stun"
 #define WEAKEN    "weaken"