update copyright notice and license description for mt19937ar.[ch]

despite the fact original authors agreed to distribute their work
under MIT license, it does not mean mt19937ar.[ch] became the work
of mruby developers. To clarify, we updated copyright and license
notice of the source files.

mrbgems/mruby-random/src/mt19937ar.c

 /*
 ** mt19937ar.c - MT Random functions
 **
-** See Copyright Notice in mruby.h
+** Copyright (C) 1997 - 2016, Makoto Matsumoto and Takuji Nishimura,
+** All rights reserved.
+**
+** Permission is hereby granted, free of charge, to any person obtaining
+** a copy of this software and associated documentation files (the
+** "Software"), to deal in the Software without restriction, including
+** without limitation the rights to use, copy, modify, merge, publish,
+** distribute, sublicense, and/or sell copies of the Software, and to
+** permit persons to whom the Software is furnished to do so, subject to
+** the following conditions:
+**
+** The above copyright notice and this permission notice shall be
+** included in all copies or substantial portions of the Software.
+**
+** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+** CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+** SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+**
+** [ MIT license: http://www.opensource.org/licenses/mit-license.php ]
+**
+** Any feedback is very welcome.
+** http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
+** email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
 */
 
 #include <mruby.h>

mrbgems/mruby-random/src/mt19937ar.h

 /*
 ** mt19937ar.h - MT Random functions
 **
-** See Copyright Notice in mruby.h
+** Copyright (C) 1997 - 2016, Makoto Matsumoto and Takuji Nishimura,
+** All rights reserved.
+**
+** Permission is hereby granted, free of charge, to any person obtaining
+** a copy of this software and associated documentation files (the
+** "Software"), to deal in the Software without restriction, including
+** without limitation the rights to use, copy, modify, merge, publish,
+** distribute, sublicense, and/or sell copies of the Software, and to
+** permit persons to whom the Software is furnished to do so, subject to
+** the following conditions:
+**
+** The above copyright notice and this permission notice shall be
+** included in all copies or substantial portions of the Software.
+**
+** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+** CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+** SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+**
+** [ MIT license: http://www.opensource.org/licenses/mit-license.php ]
+**
+** Any feedback is very welcome.
+** http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
+** email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
 */
 
 #define N 624