Fix issue 692 -- remove `varargout`

[teddychao]

Fixes #692.

Changes proposed in this pull request:

• remove varargout in remaining functions, namely
  • data_editor
  • display
  • ecg_editor
  • filtfilt
  • find_channel
  • jobman
  • load1
  • overwrite
  • prepdata
  • pulse_convert
  • pupil_pp
  • rev_dcm
  • rev_glm
  • tam

[teddychao]

Hi @dominikbach Thanks for approving this. Please kindly allow me a little time to update the description of these functions in documents.