let the library ship its own proguard rules

see also: http://google.github.io/android-gradle-dsl/1.5/com.android.build.gradle.internal.dsl.ProductFlavor.html#com.android.build.gradle.internal.dsl.ProductFlavor:consumerProguardFiles

build.gradle

@@ -19,13 +19,7 @@ android {
     defaultConfig {
         minSdkVersion 4
         targetSdkVersion Integer.parseInt(project.ANDROID_BUILD_TARGET_SDK_VERSION)
-    }
-
-    buildTypes {
-        release {
-            minifyEnabled true
-            proguardFile 'proguard.txt'
-        }
+        consumerProguardFiles 'proguard.txt'
     }
 
     lintOptions {

example/build.gradle

@@ -16,14 +16,12 @@ android {
     buildTypes {
 
         debug {
-            minifyEnabled true
-            proguardFile 'proguard.pro'
             applicationIdSuffix ".debug"
         }
 
         release {
             minifyEnabled true
-            proguardFile 'proguard.pro'
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard.pro'
         }
     }
 

example/proguard.pro

@@ -1,2 +1,17 @@
--keepattributes LineNumberTable,SourceFile
--dontoptimize
+# Add project specific ProGuard rules here.
+# By default, the flags in this file are appended to flags specified
+# in <android-sdk>/tools/proguard/proguard-android.txt
+# You can edit the include path and order by changing the proguardFiles
+# directive in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# Add any project specific keep options here:
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}