smart dates: make "this" optional

Ledger/Dates.hs

@@ -236,7 +236,7 @@ Assumes any text in the parse stream has been lowercased.
 smartdate :: GenParser Char st SmartDate
 smartdate = do
   let dateparsers = [yyyymmdd, ymd, ym, md, y, d, month, mon, today, yesterday, tomorrow,
-                     lastthisnextthing
+                     lastthisnextthing, thing
                     ]
   (y,m,d) <- choice $ map try dateparsers
   return $ (y,m,d)
@@ -339,6 +339,17 @@ lastthisnextthing = do
             
   return ("",r,p)
 
+thing :: GenParser Char st SmartDate
+thing = do
+  p <- choice $ [
+        string "day"
+       ,string "week"
+       ,string "month"
+       ,string "quarter"
+       ,string "year"
+      ]
+  return ("","this",p)
+
 periodexpr :: Day -> GenParser Char st (Interval, DateSpan)
 periodexpr rdate = choice $ map try [
                     intervalanddateperiodexpr rdate,