Unicode handling:

Removed the Perl dependencies on Encode, Encode::Locale and Unicode::Normalize.
Added dependency on boost::locale.
Added encode_path, decode_path, normalize_utf8 functions to Slic3r.xs

Slic3r.xs has been made mostly utf8 safe by using the boost::nowide library,
thanks to @alexrj for the idea.

Simplified the encode_path / decode_path stuff:
wxWidgets are unicode already, so there is no need to decode_path() from it.
Perl / win32 interfacing is non-unicode, so decode_path() is executed
on ARGV just at the beginning of the perl scripts.

xs/src/libslic3r/GCode.hpp

@@ -126,7 +126,7 @@ public:
         {}
     ~GCode() {}
 
-    bool            do_export(FILE *file, Print &print);
+    bool            do_export(Print *print, const char *path);
 
     // Exported for the helper classes (OozePrevention, Wipe) and for the Perl binding for unit tests.
     const Pointf&   origin() const { return m_origin; }
@@ -146,6 +146,8 @@ public:
     void            apply_print_config(const PrintConfig &print_config);
 
 protected:
+    bool            _do_export(Print &print, FILE *file);
+
     // Object and support extrusions of the same PrintObject at the same print_z.
     struct LayerToPrint
     {