title: Proguard - also use proguard files from modules
body: <p>My projects build.gradle looks like following:</p>
  
  <pre><code>android { 
      compileSdkVersion 22
      buildToolsVersion "22.0.1"
  
      defaultConfig {
          applicationId "..."
          minSdkVersion 15
          targetSdkVersion 22
          versionCode 1
          versionName "1.0"
      }
      buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      compile project(':androKnife')
  }
  </code></pre>
  
  <p>And my <code>androKnife</code> module does have it's own proguard file. How can I make my main project use this file as well?</p>
  
  <p>Is there some way to auto merge all proguard files of all modules, if I compile a project? Is there another way a module can specify it's proguard rules and a project can inherit it?</p>