Update version and version code

Version must be changed in:
- configure.ac
- src/windows/config.h
- android/jni/include/config.h
- android/build.gradle
- android/AndroidManifest.xml

android/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.reecedunn.espeak"
-    android:versionCode="19"
+    android:versionCode="20"
     android:versionName="1.51-dev" >
 
     <uses-feature

android/build.gradle

         minSdkVersion 14
         targetSdkVersion 26
         versionCode 20
-        versionName "1.48.15"
+        versionName "1.51-dev"
     }
 
     sourceSets {