Known issues to be handled:

Version 0.8:

- HELP procedure does not handle all keywords.

- PLOT procedure does not handle all keywords.

- !ERROR, !ERR and !ERROR_STATE are not properly set by all library
  functions

- ON_ERROR and CATCH are not fully implemented (GDL recognizes them,
  but does not perform any action, ie. in case of error, the data is
  not used).
