Enable parse and format for more types:

* year
    * month
    * day
    * weekday
    * year_month
    * month_day

test/date_test/format/misc.pass.cpp

@@ -0,0 +1,52 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+#include <cassert>
+#include <sstream>
+
+template <class T>
+void
+test(const std::string& in_fmt, const std::string& input,
+     const std::string& out_fmt, const std::string& output)
+{
+    using namespace date;
+    std::istringstream in{input};
+    T t;
+    in >> parse(in_fmt, t);
+    assert(!in.fail());
+    auto s = format(out_fmt, t);
+    assert(s == output);
+}
+
+int
+main()
+{
+    using namespace date;
+    test<year>("%Y", "2017", "%Y", "2017");
+    test<month>("%m", "3", "%m", "03");
+    test<day>("%d", "25", "%d", "25");
+    test<year_month>("%Y-%m", "2017-03", "%Y-%m", "2017-03");
+    test<year_month>("%y%m", "1703", "%Y-%m", "2017-03");
+    test<month_day>("%m/%d", "3/25", "%m/%d", "03/25");
+    test<weekday>("%w", "3", "%w", "3");
+}