Enabled proguard for release builds

app/build.gradle

@@ -19,6 +19,10 @@ android {
         vectorDrawables.useSupportLibrary = true
     }
     buildTypes {
+        release {
+            minifyEnabled true
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard'
+        }
         debug {
             applicationIdSuffix '.debug'
         }

app/proguard

@@ -0,0 +1,14 @@
+# Gson: https://github.com/google/gson/blob/master/examples/android-proguard-example/proguard.cfg
+-keepattributes Signature
+-keepattributes *Annotation*
+-dontwarn sun.misc.**
+-keep class com.sirekanyan.knigopis.model.** { *; }
+-keep class * implements com.google.gson.TypeAdapterFactory
+-keep class * implements com.google.gson.JsonSerializer
+-keep class * implements com.google.gson.JsonDeserializer
+
+# OkHttp: https://github.com/square/okhttp/blob/master/okhttp/src/main/resources/META-INF/proguard/okhttp3.pro
+-dontwarn javax.annotation.**
+-keepnames class okhttp3.internal.publicsuffix.PublicSuffixDatabase
+-dontwarn org.codehaus.mojo.animal_sniffer.*
+-dontwarn okhttp3.internal.platform.ConscryptPlatform