Change license to cc-by-sa 4.0

LICENSE

-Copyright (c) 2020 Jiri Vlasak
-
-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.
+Copyright (c) 2020 Michal Sojka
+Copyright (c) 2020 Petr Štěpán
+Copyright (c) 2020 Jan Chudoba
+Copyright (c) 2020 Jiří Záhora
+Copyright (c) 2020 Jiří Vlasák
+
+Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
+=======================================================
+
+- See: https://creativecommons.org/licenses/by-sa/4.0/
+- See also: https://creativecommons.org/licenses/by-sa/4.0/legalcode
+
+You are free to:
+
+    Share — copy and redistribute the material in any medium or format.
+
+    Adapt — remix, transform, and build upon the material for any purpose, even
+    commercially.
+
+
+Under the following terms:
+
+    Attribution — You must give appropriate credit, provide a link to the
+    license, and indicate if changes were made. You may do so in any reasonable
+    manner, but not in any way that suggests the licensor endorses you or your
+    use.
+
+    ShareAlike — If you remix, transform, or build upon the material, you must
+    distribute your contributions under the same license as the original.
+
+    No additional restrictions — You may not apply legal terms or technological
+    measures that legally restrict others from doing anything the license
+    permits.