Sourcefiles encoding option needed

[Vampire]

Pitest needs a source file encoding option.
Currently always the system default encoding is used, which often is not correct.
It is quite common to have UTF-8 encoded source files and build on Windows.
this causes corrupted source display in the report.
For example in my copyright I have Björn, but it is displayed as Björn, which means it is saved in UTF-8, but read in ISO-8859-1.

The (or at least one) culprit is org.pitest.mutationtest.tooling.DirectorySourceLocator.FileToReader#apply as it opens a new FileReader without specifying an encoding.