Added doc-blocks to the TokenReplacement plugin.

TODO:
- test replaceFromInto(..., $destination) where $destination exists (as file and as a directory)
- test the behaviour of replacing unbound tokens: do we i) keep them unchanged or do we ii) replace them with nothing?
- add FileSet to allow replaceInto to operate on fileset
- allow using a closure to map elements in the FileSet to their respective $destination name, for use with replaceFromInto
  e.g. ```replaceFromInto($fileset, function($file) { return str_replace('*.dist', '', $file->getFilename()); });```