bump to version 15

AndroidManifest.xml

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
       package="org.galexander.sshd"
-      android:versionCode="14"
-      android:versionName="14">
+      android:versionCode="15"
+      android:versionName="15">
     <uses-sdk android:minSdkVersion="7" android:targetSdkVersion="11" />
     <uses-permission android:name="android.permission.INTERNET" />
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

doc/index.html

@@ -111,6 +111,7 @@ commandline.</dd>
 <h2>Change Log</h2>
 
 <ul>
+<li> <b>2016/10/17 Version 15:</b> Fix crash on pre-Nougat versions of Android.
 <li> <b>2016/10/16 Version 14:</b> Support single-use passwords for
 bootstrapping.
 <li> <b>2016/10/16 Version 13:</b> Support foreground service (fewer