Add a mob extension plugin for walking to entities

Adds a new mob extension plugin which creates a walk_to() method on
Mobs to allow walking to another entity (accounting for the size of the
entity) with an optional facing position.

data/plugins/entity/mob/walk-to/plugin.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<plugin>
+    <id>mob-walk-to</id>
+    <version>0.1</version>
+    <name>Mob path generation</name>
+    <description>Adds a mixin for making mobs walk to another entity.</description>
+    <authors>
+        <author>Gary Tierney</author>
+    </authors>
+    <scripts>
+        <script>walk_to.rb</script>
+    </scripts>
+    <dependencies>
+        <dependency>mob-extension</dependency>
+    </dependencies>
+</plugin>