markdown: add button and drawable resource

app/src/main/res/drawable/ic_markdown.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24"
+        android:viewportHeight="24">    
+    <path
+        android:strokeColor="#000"
+        android:strokeWidth="1.1348"
+        android:pathData="M1.9179 5.1162h20.199c0.62866 0 1.1348 0.50611 1.1348 1.1348v11.121c0 0.62866-0.50611 1.1348-1.1348 1.1348h-20.199c-0.62866 0-1.1348-0.50611-1.1348-1.1348v-11.121c0-0.62866 0.50611-1.1348 1.1348-1.1348z" />
+    <path
+        android:fillColor="#000000"
+        android:strokeWidth=".11348"
+        android:pathData="M3.62 15.669v-7.7164h2.2695l2.2695 2.8369 2.2695-2.8369h2.2695v7.7164h-2.2695v-4.4256l-2.2695 2.8369-2.2695-2.8369v4.4256zm14.185 0-3.4043-3.7447h2.2695v-3.9717h2.2695v3.9717h2.2695z" />
+</vector>

app/src/main/res/layout/activity_compose.xml

@@ -324,6 +324,17 @@
             android:tooltipText="@string/action_schedule_toot"
             app:srcCompat="@drawable/ic_access_time" />
 
+        <ImageButton
+            android:id="@+id/composeMarkdownButton"
+            style="?attr/image_button_style"
+            android:layout_width="36dp"
+            android:layout_height="36dp"
+            android:layout_marginEnd="4dp"
+            android:contentDescription="@string/action_markdown"
+            android:padding="4dp"
+            android:tooltipText="@string/action_markdown"
+            app:srcCompat="@drawable/ic_markdown" />
+
         <Space
             android:layout_width="0dp"
             android:layout_height="wrap_content"

app/src/main/res/values/strings.xml

@@ -131,6 +131,7 @@
     <string name="action_open_reblogger">Open boost author</string>
     <string name="action_open_reblogged_by">Show boosts</string>
     <string name="action_open_faved_by">Show favorites</string>
+    <string name="action_markdown">Markdown</string>
 
     <string name="title_hashtags_dialog">Hashtags</string>
     <string name="title_mentions_dialog">Mentions</string>