Repl prints listy things with sugar

Searches for applications of "Nil" and "::" and prints them accordingly.
Print Nats as numerals

Might be more controversial than the list resugaring, since it's very
ad-hoc, but I can't be the only one sick of counting S's. :)
Fix parameter identification in data declarations
Fixes issue #259
Move parsing of comprehensions
Fixes issue #178
Make 'count' partial/abstract to prevent compile-time reduction
Deals with issue #171
Added bare bones implementations of maps and sets
Fix :t for metavariables
Fixes issue #280
Generalization of Decidable
general axioms for Preorders and Posets
instance for less-than-equal on Nat
Renamed Map and Set to SortedMap and SortedSet
Merge branch 'maps_and_sets' of https://github.com/DanielWaterworth/Idris-dev into DanielWaterworth-maps_and_sets
Merge branch 'DecidableOrder' of https://github.com/JanBessai/Idris-dev into JanBessai-DecidableOrder
Add Decidable.Decidable and Decidable.Order to base.ipkg
Don't allow unification problems to be introduced in :p mode
Update version number in tutorial
Fix scoping rules on lhs of with clause