Add SoLoud license

Author: tmikov

LICENSE_soloud

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+SoLoud contains various third party libraries which vary in licenses,
+but are all extremely liberal; no attribution in binary form is required.
+For more information, see SoLoud manual or http://soloud-audio.com/legal.html
+
+SoLoud proper is licensed under the zlib/libpng license:
+
+SoLoud audio engine
+Copyright (c) 2013-2018 Jari Komppa
+
+This software is provided 'as-is', without any express or implied
+warranty. In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+   1. The origin of this software must not be misrepresented; you must not
+   claim that you wrote the original software. If you use this software
+   in a product, an acknowledgment in the product documentation would be
+   appreciated but is not required.
+
+   2. Altered source versions must be plainly marked as such, and must not be
+   misrepresented as being the original software.
+
+   3. This notice may not be removed or altered from any source
+   distribution.