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`.