add missing file header

bson/src/main/scala/codes/bytes/hammersmith/bson/codecs/BSONCodec.scala

@@ -1,3 +1,19 @@
+/**
+  * Copyright (c) 2011-2015 Brendan McAdams <http://bytes.codes>
+  *
+  * Licensed under the Apache License, Version 2.0 (the "License");
+  * you may not use this file except in compliance with the License.
+  * You may obtain a copy of the License at
+  *
+  * http://www.apache.org/licenses/LICENSE-2.0
+  *
+  * Unless required by applicable law or agreed to in writing, software
+  * distributed under the License is distributed on an "AS IS" BASIS,
+  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  * See the License for the specific language governing permissions and
+  * limitations under the License.
+  *
+  */
 package codes.bytes.hammersmith.bson.codecs
 
 import codes.bytes.hammersmith.bson.types._