Add copyright headers and contributors list

Add proper copyright notices to all source files with accurate date
ranges per contributor based on git history. Add contributors to
composer.json authors and README.

composer.json

@@ -10,6 +10,21 @@
             "name": "Boris Gulay",
             "email": "boris@gulay.name",
             "role": "Original Developer"
+        },
+        {
+            "name": "Christian Landvogt",
+            "email": "chris@lvgt.de",
+            "role": "Contributor"
+        },
+        {
+            "name": "Gergely Papp",
+            "email": "telirium@gmail.com",
+            "role": "Contributor"
+        },
+        {
+            "name": "Laurent Dinclaux",
+            "email": "laurent@gecka.nc",
+            "role": "Maintainer"
         }
     ],
     "repositories": [