Add simple test on filename extension to decide its treatment

This is a temporary construction to allow language tests while still checking
that nothing is broken (i.e. w/o language)

src/main.cpp

@@ -27,11 +27,17 @@
 
 #include <limits>
 #include <map>
+#include <regex>
 
 int main(int argc, char *argv[])
 {
   std::string filename = initialize(argc, argv);
+
+   std::regex gmsh_regex("(.*).msh");
+   if (not std::regex_match(filename, gmsh_regex))  {
       parser(filename);
+      return 0;
+   }
 
   std::map<std::string, double> method_cost_map;