Add Wavenumber axis

ha2=addinvcmaxis(DecPlaces,Unit,ha)
Adds a 'Wavenumber (cm^{-1})' axis on top of current graph where the the
x-axis is in nm or µm. The xlabel should be specified with unit before
running addinvcmaxis(), otherwise it can be specified as
addinvcmaxis(DecPlaces,Unit).

Use:
addinvcmaxis() if unit of wavelength is specified in xlabel or,
addinvcmaxis(DecPlaces) where DecPlaces = decimal places, 0=Default will display waveno. without decimals, or
addinvcmaxis(DecPlaces,Unit) where 'Unit' is the unit in (m), i.e. if the graph is in nm Unit=1e-9, or
addinvcmaxis(DecPlaces,Unit,ha) if you want to add the axis to a different axis than the current, i.e., gca.
cc micke.malmstrom@gmail.com
Version 2015-09-24