Add .clang-format and apply it

2015/puzzle-01-01.cc

@@ -2,7 +2,8 @@
 #include <iostream>
 #include <string>
 
-int main(int argc, char **argv) {
+int main(int argc, char** argv)
+{
   for (std::string line; std::getline(std::cin, line);) {
     int floor = 0;
     for (auto c : line) {