add date formats found in jekyll posts

The first added is definitely in jekyll. The second, I believe, happens,
too.

caste.go

@@ -433,6 +433,8 @@ func StringToDate(s string) (time.Time, error) {
 		"02 Jan 06 15:04 MST",
 		"2006-01-02",
 		"02 Jan 2006",
+		"2006-01-02 15:04:05 -07:00",
+		"2006-01-02 15:04:05 -0700",
 	})
 }