[DOXIA-386] Snippet Macro: Reference file does not support UTF-8 file format to generate the page garbage

- Make clirr happy with a single-arg ctor
- Add Unicode text to the testSnippet.txt in Russian to test the 'encoding' parameter. Text reads "This snippet is in Unicode format (UTF-8)"

git-svn-id: https://svn.apache.org/repos/asf/maven/doxia/doxia/trunk@1544338 13f79535-47bb-0310-9956-ffa450edef68