Added additional command line options
Some command line options (like --diff and --diff-branch cannot be
specified in the scalafmt configuration file. This makes a change so
they can be passed in from the pom.xml as follows:
<plugin>
<groupId>org.antipathy</groupId>
<artifactId>mvn-scalafmt</artifactId>
<version>0.2</version>
<configuration>
<parameters>--diff-branch some-branch</paramaters>
<configLocation>${project.basedir}/path/to/scalafmt.conf</configLocation>
</configuration>
</plugin>