Add LICENSE file.

LICENSE.txt

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+Microsoft Public License (Ms-PL)
+
+This license governs use of the accompanying software. If you use the software,
+you accept this license. If you do not accept the license, do not use the
+software.
+
+1. Definitions
+
+The terms "reproduce," "reproduction," "derivative works," and "distribution"
+have the same meaning here as under U.S. copyright law.
+
+A "contribution" is the original software, or any additions or changes to the
+software.
+
+A "contributor" is any person that distributes its contribution under this
+license.
+
+"Licensed patents" are a contributor's patent claims that read directly on its
+contribution.
+
+2. Grant of Rights
+
+(A) Copyright Grant- Subject to the terms of this license, including the license
+conditions and limitations in section 3, each contributor grants you a
+non-exclusive, worldwide, royalty-free copyright license to reproduce its
+contribution, prepare derivative works of its contribution, and distribute its
+contribution or any derivative works that you create.
+
+(B) Patent Grant- Subject to the terms of this license, including the license
+conditions and limitations in section 3, each contributor grants you a
+non-exclusive, worldwide, royalty-free license under its licensed patents to
+make, have made, use, sell, offer for sale, import, and/or otherwise dispose of
+its contribution in the software or derivative works of the contribution in the
+software.
+
+3. Conditions and Limitations
+
+(A) No Trademark License- This license does not grant you rights to use any
+contributors' name, logo, or trademarks.
+
+(B) If you bring a patent claim against any contributor over patents that you
+claim are infringed by the software, your patent license from such contributor
+to the software ends automatically.
+
+(C) If you distribute any portion of the software, you must retain all
+copyright, patent, trademark, and attribution notices that are present in the
+software.
+
+(D) If you distribute any portion of the software in source code form, you may
+do so only under this license by including a complete copy of this license with
+your distribution. If you distribute any portion of the software in compiled or
+object code form, you may only do so under a license that complies with this
+license.
+
+(E) The software is licensed "as-is." You bear the risk of using it. The
+contributors give no express warranties, guarantees or conditions. You may have
+additional consumer rights under your local laws which this license cannot
+change. To the extent permitted under your local laws, the contributors exclude
+the implied warranties of merchantability, fitness for a particular purpose and
+non-infringement.