java 8 support and support for passing configuration to Eclipse compiler

Also support for passing compilerArguments like the below. These are prefixed by with a '-' by [AbstractCompilerMojo](https://github.com/apache/maven-plugins/blob/trunk/maven-compiler-plugin/src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java#L564) 
```
 <configuration>
       <compilerId>eclipse</compilerId>
       <source>1.8</source>
       <target>1.8</target>
        <compilerArguments>
                <org.eclipse.jdt.core.compiler.compliance>1.8</org.eclipse.jdt.core.compiler.compliance>
         </compilerArguments>
 </configuration>
```