Feature #43 - Relative dates: +3d, -2w

- Added feature #43, now task supports relative dates like '3wks',
  '1 month', '4d' for 'due', 'wait' and 'until' dates.  Essentially
  durations are now allowed where dates are expected, and are treated
  as relative to the current date/time.

doc/man/task.1

@@ -335,7 +335,7 @@ Attribute modifiers improve filters.  Supported modifiers are:
 .br
 .B  isnt       (synonym not)
 .br
-.B  has        (synonym contain)
+.B  has        (synonym contains)
 .br
 .B  hasnt
 .br
@@ -374,11 +374,17 @@ task ... due:today
 .br
 task ... due:yesterday
 .br
-task ...  due:tomorrow
+task ... due:tomorrow
 
 .TP
 Day number with ordinal
 task ... due:23rd
+.br
+task ... due:3wks
+.br
+task ... due:1day
+.br
+task ... due:9hrs
 
 .TP
 End of week (Friday), month and year