Adding license

LICENSE.md

+Copyright 2015-2016 Institute of Technical Acoustics, RWTH Aachen University
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use files of this project 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.
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