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