add package.xml

Add a file package.xml allowing to compile with catkin.

package.xml

+<?xml version="1.0"?>
+<package format="2">
+  <name>vision_utils</name>
+  <version>0.0.0</version>
+  <description>The vision_utils package</description>
+
+  <maintainer email="asantamaria@iri.upc.edu">Angel Santamaria</maintainer>
+
+  <author>Angel Santamaria</author>
+
+  <license>GPL-3.0</license>
+
+  <buildtool_depend>cmake</buildtool_depend>
+
+  <build_depend>OpenCV</build_depend>
+  <build_depend>YAMLCPP</build_depend>
+
+  <export>
+    <build_type>cmake</build_type>
+  </export>
+</package>