Custom BuildConfig constants from the plugin configuration

https://groups.google.com/forum/?fromgroups#!topic/maven-android-developers/ZvFtLNufSXU

This plugin configuration:

    <configuration>
        <buildConfigConstants>
            <constant>
                <name>TEST_NUMBER</name>
                <type>int</type>
                <value>123</value>
            </constant>
            <constant>
                <name>SERVER</name>
                <type>String</type>
                <value>http://app-staging.herokuap.com</value>
            </constant>
        </buildConfigConstants>
    </configuration>

Generates the following BuildConfig.java:

    package app.package;
    
    public final class BuildConfig {
      public static final boolean DEBUG = true;
      public static final int TEST_NUMBER = 123;
      public static final String SERVER = "http://app-staging.herokuap.com";
    }