Add new licenses

Author: Mizunashi Mana

.plugin_includes

@@ -2,6 +2,9 @@ conf
 lang
 src
 vendor
-LICENSE
+README.md
+LICENSE.txt
+LICENSE.Apache-2.0
+LICENSE.GPL-2.0-or-later
 plugin.info.txt
 syntax.php

LICENSE

@@ -0,0 +1,13 @@
+Copyright 2018- Mizunashi Mana
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+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.

LICENSE.Apache-2.0

@@ -0,0 +1 @@
+Apache-2.0 OR GPL-2.0-or-later

LICENSE.GPL-2.0-or-later

@@ -10,10 +10,13 @@ See <https://www.dokuwiki.org/plugin:mdpage>.
 
 ## Report a bug / Contribute a fix
 
-See [Contributing Guide](CONTRIBUTING.md).
+See [Contributing Guide](https://github.com/mizunashi-mana/dokuwiki-plugin-mdpage/blob/master/CONTRIBUTING.md).
 
 ## License
 
-This plugin is licensed under [the MIT License](LICENSE).
+This work is dual-licensed under [the Apache 2.0 License](https://github.com/mizunashi-mana/dokuwiki-plugin-mdpage/blob/master/LICENSE.Apache-2.0) and [the GPL 2.0 (or any later version)](https://github.com/mizunashi-mana/dokuwiki-plugin-mdpage/blob/master/LICENSE.GPL-2.0-or-later).
+You are free to pick which one suits your needs.
 
 * Using [cebe/markdown](https://github.com/cebe/markdown) to parse Markdown texts under [the MIT License](https://github.com/cebe/markdown/blob/master/LICENSE).
+
+Notice: DokuWiki is licensed under [the GPL 2.0](https://github.com/splitbrain/dokuwiki/blob/master/COPYING).  This license cannot be compatible with the Apache 2.0 License and the GPL 3.0.  See also: https://www.gnu.org/licenses/license-list.html .

LICENSE.txt

@@ -7,7 +7,10 @@
         "plugin",
         "markdown"
     ],
-    "license": "MIT",
+    "license": [
+        "Apache-2.0",
+        "GPL-2.0-or-later"
+    ],
     "authors": [
         {
             "name": "Mizunashi Mana",