Move loading of options to separate function

[BSchilperoort]

Currently, the options struct is loaded in on the following lines:

STEMMUS_SCOPE/src/STEMMUS_SCOPE.m

Lines 67 to 97 in b43b475

	if length(parameter_file)>1, useXLSX = 0; else useXLSX = 1; end
	if ~useXLSX
	run([path_input parameter_file{1}])
	options.calc_ebal = N(1); % calculate the energy balance (default). If 0, then only SAIL is executed!
	options.calc_vert_profiles = N(2); % calculate vertical profiles of fluxes
	options.calc_fluor = N(3); % calculate chlorophyll fluorescence in observation direction
	options.calc_planck = N(4); % calculate spectrum of thermal radiation
	options.calc_directional = N(5); % calculate BRDF and directional temperature
	options.calc_xanthophyllabs = N(6); % include simulation of reflectance dependence on de-epoxydation state
	options.calc_PSI = N(7); % 0: optipar 2017 file with only one fluorescence spectrum vs 1: Franck et al spectra for PSI and PSII
	options.rt_thermal = N(8); % 1: use given values under 10 (default). 2: use values from fluspect and soil at 2400 nm for the TIR range
	options.calc_zo = N(9);
	options.soilspectrum = N(10); %0: use soil spectrum from a file, 1: simulate soil spectrum with the BSM model
	options.soil_heat_method = N(11); % 0: calculated from specific heat and conductivity (default), 1: empiricaly calibrated, 2: G as constant fraction of soil net radiation
	options.Fluorescence_model = N(12); %0: empirical, with sustained NPQ (fit to Flexas' data); 1: empirical, with sigmoid for Kn; 2: Magnani 2012 model
	options.calc_rss_rbs = N(13); % 0: calculated from specific heat and conductivity (default), 1: empiricaly calibrated, 2: G as constant fraction of soil net radiation
	options.apply_T_corr = N(14); % correct Vcmax and rate constants for temperature in biochemical.m
	options.verify = N(15);
	options.save_headers = N(16); % write headers in output files
	options.makeplots = N(17);
	options.simulation = N(18); % 0: individual runs (specify all input in a this file)
	% 1: time series (uses text files with meteo input as time series)
	% 2: Lookup-Table (specify the values to be included)
	% 3: Lookup-Table with random input (specify the ranges of values)
	else
	options = io.readStructFromExcel([path_input char(parameter_file)], 'options', 3, 1);
	end
	if options.simulation>2 || options.simulation<0, fprintf('\n simulation option should be between 0 and 2 \r'); return, end

However, to clean up the main script we would like to move this to a separate function, for example in the package src/+io.