First full commit of plugin system

doc/Plugin_System.md

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+# Developing for the Plugin System
+
+This documentation will hopefully give you a basis for how to write a plugin for LibreNMS.
+
+A test plugin is available on GitHib: https://github.com/laf/Test
+
+Plugins need to be installed into html/plugins
+
+The structure of a plugin is follows:
+
+```
+html/plugins
+            /PluginName
+                       /PluginName.php
+                       /PluginName.inc.php
+```
+
+The above structure is checked before a plugin can be installed.
+
+All files / folder names are case sensitive and must match.
+
+PluginName - This is a directory and needs to be named as per the plugin you are creating.
+
+PluginName.php - This file is used to process calls into the plugin from the main LibreNMS install.
+                 Here only functions within the class for your plugin that LibreNMS calls will be executed.
+                 For a list of currently enabled system hooks, please see further down.
+                 The minimum code required in this file is (replace Test with the name of your plugin):
+```
+<?php
+
+class Test {
+}
+
+?>
+```
+
+PluginName.inc.php - This file is the main included file when browsing to the plugin itself.
+                     You can use this to display / edit / remove whatever you like.
+                     The minimum code required in this file is:
+```
+<?php
+
+?>
+```
+
+### System Hooks ###
+
+System hooks are called as functions within your plugin class, so for example to create a menu entry within the PLugin dropdown you would do:
+
+```
+  public function menu() {
+    echo('<li><a href="plugin/p='.get_class().'">'.get_class().'</a></li>');
+  }
+```
+
+This would then add the name and a link to your plugin.
+
+The following system hooks are currently available:
+
+menu()
+* This is called to build the plugin menu system and you can use this to link to your plugin (you don't have to).