old_contents: ext2lang = {
      '.cpp': 'c++',
      '.c': 'c',
  }
  
new_contents: ext2lang = {
      '.c'  : 'c',
      '.cpp': 'c++',
      '.cc' : 'c++',
      '.cp' : 'c++',
      '.cxx': 'c++',
      '.CPP': 'c++',
      '.c++': 'c++',
      '.C'  : 'c++',
  }
  
subject: Support more C++ extensions by default