android: raise minSdkVersion to 21

The number of MPD installs on Android < 5.0 is negligible, and that
API version introduces lots of useful features for MPD.

android/AndroidManifest.xml

@@ -5,7 +5,7 @@
           android:versionCode="20"
           android:versionName="0.20.21">
 
-  <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="17"/>
+  <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="21"/>
 
   <application android:icon="@drawable/icon" android:label="@string/app_name">
     <activity android:name=".Main"

android/build.py

@@ -65,7 +65,7 @@ class AndroidNdkToolchain:
         self.build_path = build_path
 
         ndk_arch = abi_info['ndk_arch']
-        android_api_level = '14'
+        android_api_level = '21'
         ndk_platform = 'android-' + android_api_level
 
         # select the NDK compiler

android/src/Main.java

@@ -49,7 +49,7 @@ public class Main extends Activity implements Runnable {
 			TextView tv = new TextView(this);
 			tv.setText("Failed to load the native MPD libary.\n" +
 				   "Report this problem to us, and include the following information:\n" +
-				   "ABI=" + Build.CPU_ABI + "\n" +
+				   "SUPPORTED_ABIS=" + String.join(", ", Build.SUPPORTED_ABIS) + "\n" +
 				   "PRODUCT=" + Build.PRODUCT + "\n" +
 				   "FINGERPRINT=" + Build.FINGERPRINT + "\n" +
 				   "error=" + Loader.error);