copy2clipboard Plugin for DokuWiki

Add button to copy `<code>` and `<file>` content to clipboard.

All documentation for this plugin can be found at
https://github.com/schplurtz/dokuwiki-plugin-copy2clipboard

Please refer to https://www.dokuwiki.org/plugins for additional info
on how to install plugins in DokuWiki.

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Resources I've used while trying to write this little piece of code. Without
them, I would not have been able to write this. I voted up the solutions when
appropriate.

*  https://codetonics.com/javascript/detect-document-ready/
*  https://www.dokuwiki.org/devel:jqueryfaq
*  https://flaviocopes.com/clipboard-api/ Thanks a million.
*  https://www.w3schools.com/jsref/prop_node_parentelement.asp
*  https://stackoverflow.com/a/35213639/1831273 innerText vs textContent
*  https://stackoverflow.com/a/10371757/1831273 innetText or textContent
*  https://www.w3schools.com/howto/howto_js_add_class.asp
*  https://stackoverflow.com/a/11701129/1831273 first child of given type
*  https://css-tricks.com/absolute-relative-fixed-positioining-how-do-they-differ/ a must read
*  https://css-tricks.com/position-sticky-2/

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Copyright (C) Schplurtz le Déboulonné <Schplurtz@laposte.net>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

See the LICENSE file for details