Add generate_days script

- Add generate_days script to generate templated files for an advent of
  code year.
- Optimize the fetch.sh script (remove awk usage)

Template.cpp

@@ -0,0 +1,31 @@
+#include "common/aoc.h"
+
+namespace y$1::day$2
+{
+  REGISTER_DAY($1, Day$2, std::vector<int>, int);
+
+  REGISTER_TEST_EXAMPLE($1, Day$2, ExampleInput, 1, 0);
+  REGISTER_TEST($1, Day$2, Input, 1, 0);
+  REGISTER_TEST_EXAMPLE($1, Day$2, ExampleInput, 2, 0);
+  REGISTER_TEST($1, Day$2, Input, 2, 0);
+
+  READ_INPUT(input)
+  {
+    std::vector<int> vec;
+    std::string str;
+    while (getline(input, str))
+    {
+    }
+    return vec;
+  }
+
+  OUTPUT1(input)
+  {
+    return 0;
+  }
+
+  OUTPUT2(input)
+  {
+    return 0;
+  }
+}