Turn debug printing off by default

Otherwise stderr is spammed with harmless runtime error prints,
since we generate code like

  try
    ..
  with Runtime_error(_, _) ->
    (* that's ok, do something else *)

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #23 from djs55/turn-off-debug-for-release

Turn debug printing off by default