add license files for components of cereal

Signed-off-by: Adam Miartus <adam.miartus@softhows.eu>

include/cereal/external/LICENSE

@@ -0,0 +1,21 @@
+Copyright (C) 2004-2008 René Nyffenegger
+
+This source code is provided 'as-is', without any express or implied
+warranty. In no event will the author 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 source code must not be misrepresented; you must not
+  claim that you wrote the original source code. If you use this source code
+  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 source code.
+
+3. This notice may not be removed or altered from any source distribution.
+
+René Nyffenegger rene.nyffenegger@adp-gmbh.ch

include/cereal/external/rapidjson/LICENSE

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+Tencent is pleased to support the open source community by making RapidJSON available.
+
+Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
+
+Licensed under the MIT License (the "License"); you may not use this file except
+in compliance with the License. You may obtain a copy of the License at
+
+http://opensource.org/licenses/MIT
+
+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.

include/cereal/external/rapidjson/msinttypes/LICENSE

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+ISO C9x  compliant stdint.h for Microsoft Visual Studio
+Based on ISO/IEC 9899:TC2 Committee draft (May 6, 2005) WG14/N1124 
+
+ Copyright (c) 2006-2013 Alexander Chemeris
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+  1. Redistributions of source code must retain the above copyright notice,
+     this list of conditions and the following disclaimer.
+
+  2. Redistributions in binary form must reproduce the above copyright
+     notice, this list of conditions and the following disclaimer in the
+     documentation and/or other materials provided with the distribution.
+
+  3. Neither the name of the product nor the names of its contributors may
+     be used to endorse or promote products derived from this software
+     without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
+WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.