Add factorial, gcd, and lcm to Nat.
Add WriterT.
Add ReaderT.
More functions for Reader and Writer.
Add RWST.
Allow hints to be given to proof search

:ps now takes an optional list of names to be used as hints in the
proof search.
Make libffi support a cabal flag

It has quite a specific use at the minute and can make installation a
bit awkward, so this means it's not required for installation.
LLVM and FFI flags default to off

This is primarily so that installation is easier for new users. Users
who want these features can of course turn them on easily enough!

(Ideally, we want binary packages which will switch everything on.)
Ask travis to install optional dependencies
Added warning in case Idris is compiled without libffi support
Add :apc for adding "proof style" declarations

That is, :apc on
plus_comm : (m, n : Nat) -> (plus m n = plus n m)

will add the caluse
(plus m n = plus n m) <== plus_comm = ?plus_comm_rhs

where m and n can be case split as normal
Merge pull request #570 from folone/master

Add factorial, gcd, and lcm to Nat.
Merge pull request #571 from folone/topic/writer

RWST
Merge pull request #574 from david-christiansen/ffiwarn

Added warning in case Idris is compiled without libffi support
Update CHANGELOG and verison number
Add new editor commands to tab completion
Whitespace cleanup.
Merge pull request #575 from david-christiansen/tab-new-cmds

Add new editor commands to tab completion
Merge pull request #576 from folone/master

Whitespace cleanup.
Add quick and dirty Emacs interactive editing support