Apache License

Added the apache license to all source files, accounting for authors. Also added a license.md containing the apache license + contributors.md listing all contributors.

src/stub/stub.asm

@@ -1,3 +1,17 @@
+;  Copyright 2021 Kieron Morris
+;
+;  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.
+
 ;
 ; Kernel stub
 ;