Add test for replacement format containing unicode chars

Python Tests for unicode replacement strings also added
Add fromChars() to CharTraitsT, to convert from const char* to string_type

This is a cheap fix, to ensure that match_results::format() gets the right
encoding.  It'd be nice to fix these converters such that we only do the
conversion rather than the multiple alloc/dealloc/convert-to-string
mess that we're doing now.
Merge branch 'fix-unicode-replacements'