Enable setting the file encoding option

[lespea]

Not sure if I just don't understand how to transfer that setting down through sbt (like q or w) but I couldn't get it to work; had to resort to modifying the sbt launcher to make java open everything open in UTF-8.

[evanbennett]

I am attempting to create a pull request for this as I require the functionality.

It appears that I should only need to replace None with a setting's value on:

scalastyle-sbt-plugin/src/main/scala/org/scalastyle/sbt/Plugin.scala

Line 204 in fc584ba

new ScalastyleChecker().checkFiles(configuration, Directory.getFiles(None, filesToProcess, Nil))

I am planning on creating a new inputFile[Codec|Charset|Encoding] setting which will be Option[scala.io.Codec|java.nio.charset.Charset|String].

Do you have a preference of: Codec (scala); Charset(java); Encoding (String)?