Issue 356

This is an initial request for comments for introducing multi-dex support in the Jayway plugin.

The usage currently is:

    <dex>
        <multiDex>true</multiDex>
        <mainDexList>/Users/path/classes.txt</mainDexList>
        <minimalMainDex>true</minimalMainDex>
    </dex>

I'm thinking

    <dex>
        ... dex options...
        <multiDex>
            <mainDexList>/Users/path/classes.txt</mainDexList>
            <minimalMainDex>true</minimalMainDex>
        </multiDex>
    </dex>

Is probably nicer.

For simplicity it does not support the configuration of archive types, seems an unnecessary configuration option really. 
If there is any consensus on the usage I can wrap up with some better error handling and testing.
No need to change this