adding some new proguard rules

app/proguard-rules.pro

@@ -1,21 +1,3 @@
-# Add project specific ProGuard rules here.
-# By default, the flags in this file are appended to flags specified
-# in $ANDROID_HOME/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 *;
-#}
-
 # Joda
 -dontwarn org.joda.time.**
 
@@ -23,4 +5,10 @@
 -dontwarn com.google.common.**
 
 -renamesourcefileattribute SourceFile
--keepattributes SourceFile, LineNumberTable, Exceptions
+-keepattributes SourceFile, LineNumberTable, Signature, RuntimeVisibleAnnotations,AnnotationDefault
+
+-keep class com.simplemobiletools.calendar.models.** { *; }
+
+-keepclassmembers class * {
+  @com.google.api.client.util.Key <fields>;
+}