Add Kotlin code sample

kotlin_demo/kotlin_demo.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module type="PLUGIN_MODULE" version="4">
+  <component name="DevKit.ModuleBuildProperties" url="file://$MODULE_DIR$/resources/META-INF/plugin.xml" />
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/resources" type="java-resource" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>

kotlin_demo/resources/META-INF/plugin.xml

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+<idea-plugin version="2">
+  <id>org.jetbrains</id>
+  <name>kotlin_demo</name>
+  <version>1.0</version>
+  <vendor email="support@yourcompany.com" url="http://www.yourcompany.com">YourCompany</vendor>
+
+  <description><![CDATA[
+      Enter short description for your plugin here.<br>
+      <em>most HTML tags may be used</em>
+    ]]></description>
+
+  <change-notes><![CDATA[
+      Add change notes here.<br>
+      <em>most HTML tags may be used</em>
+    ]]>
+  </change-notes>
+
+  <!-- please see http://www.jetbrains.org/intellij/sdk/docs/basics/getting_started/build_number_ranges.html for description -->
+  <idea-version since-build="141.0"/>
+
+  <!-- please see http://www.jetbrains.org/intellij/sdk/docs/basics/getting_started/plugin_compatibility.html
+       on how to target different products -->
+  <!-- uncomment to enable plugin in all products
+  <depends>com.intellij.modules.lang</depends>
+  -->
+
+  <extensions defaultExtensionNs="com.intellij">
+    <!-- Add your extensions here -->
+  </extensions>
+
+  <actions>
+    <group id="MyPlugin.TestMeu" text="Greeting" description="Greeting menu">
+      <add-to-group group-id="MainMenu" anchor="last"  />
+      <action id="Myplugin.Textboxes" class="HelloAction" text="Hello" description="Says hello" />
+    </group>
+  </actions>
+
+</idea-plugin>

kotlin_demo/src/HelloAction.kt

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+import com.intellij.openapi.actionSystem.AnAction
+import com.intellij.openapi.actionSystem.AnActionEvent
+import com.intellij.openapi.actionSystem.PlatformDataKeys
+import com.intellij.openapi.ui.Messages
+
+class HelloAction : AnAction("Hello") {
+    override fun actionPerformed(event: AnActionEvent) {
+        val project = event.getData(PlatformDataKeys.PROJECT)
+        Messages.showMessageDialog(project, "Hello from Kotlin!", "Greeting", Messages.getInformationIcon())
+    }
+}