Enable minification for release build.

This reduces result apk size around 2x times.

Signed-off-by: Yahor Berdnikau <egorr.berd@gmail.com>

ultrasonic/build.gradle

@@ -19,8 +19,11 @@ android {
 
     buildTypes {
         release {
-            minifyEnabled false
+            minifyEnabled true
-            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
+            proguardFiles getDefaultProguardFile('proguard-android.txt'),
+                    'minify/proguard-okhttp.pro',
+                    'minify/proguard-retrofit.pro',
+                    'minify/proguard-jackson.pro'
         }
         debug {
             minifyEnabled false

ultrasonic/minify/proguard-jackson.pro

@@ -0,0 +1,11 @@
+#### From Jackson
+
+-keepattributes *Annotation*,EnclosingMethod,Signature
+-keepnames class com.fasterxml.jackson.** {
+*;
+}
+-keepnames interface com.fasterxml.jackson.** {
+    *;
+}
+-dontwarn com.fasterxml.jackson.databind.**
+-keep class org.codehaus.** { *; }

ultrasonic/minify/proguard-okhttp.pro

@@ -0,0 +1,8 @@
+#### From okhttp
+
+-dontwarn okhttp3.**
+-dontwarn okio.**
+-dontwarn javax.annotation.**
+-dontwarn org.conscrypt.**
+# A resource is loaded with a relative path so the package of this class must be preserved.
+-keepnames class okhttp3.internal.publicsuffix.PublicSuffixDatabase

ultrasonic/minify/proguard-retrofit.pro

@@ -0,0 +1,10 @@
+#### From retrofit
+
+# Retain generic type information for use by reflection by converters and adapters.
+-keepattributes Signature
+# Retain service method parameters.
+-keepclassmembernames,allowobfuscation interface * {
+    @retrofit2.http.* <methods>;
+}
+# Ignore annotation used for build tooling.
+-dontwarn org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement