Feature : Allow configure report output and support jUnit/xUnit output file

To allow Silly to be frinedly to use on any IDE, must allow to output some well know report format like jUnit/xUnit XML files.

I propose, splitting the code on a few files and create a interface Reporter that could be implemented by any report format that we desire to support. Initially being console (the actual Silly output format to STDOUT) and xUnit.

To allow to the users to use any reporter that like, I suggest adding a launch parameter "--reporter" that accepts a list of coma separate strings with the name of the desired reporters to be used (aka, console and xUnit). If it's omitted , Silly uses the "console" reporter.

This whole feature it's a key feature (making easy to use on a IDE) would be a nice improvement of DLang tooling.

I'm implementing this on my fork of Silly.