Remove -Werror in Output.hs due to ErrorT

As far as I can tell, we can't replace ErrorT with ExceptT yet because
there's a missing MonadException instance in Haskeline. Also, the
dependencies we have set are causing a build failure on travis due to
the -Werror.

Proper fixes welcome! This is noted in issue #1780
Updates to idrislang.sty
Work around bug in glibc 2.11
Several updates to idrislang.sty

+ Removal of numbers package option. Listing styles must be set either globally using `\lstset{}` or per code or listings environment options.
+ Addition of a beamer style.
+ Inclusion of the `:pprint` LaTeX formatting commands. No more need to copy everything from the result of `:pprint`, just the code snippet.
  + command chars for fancy verbatim has been set globally.
+ Option to change spacing command, useful for cases where line spacing is changed via different commands. For example: memoir has `\SingleSpacing`, setspace has `\singlespacing`.
Look in binders when building size change graph

Fixes #1781
Support for inductive-inductive types

Add constructors to context immediately after elaborating, rather than
adding the whole data type at once, so that later constructors can use
them. Fixes #1757.
Merge pull request #1783 from jfdm/contrib/updates

Updates to idrislang.sty
Merge pull request #1782 from mietek/master

Work around bug in glibc 2.11