Read ngspice MOD

I removed assert instructions to keep some backwards compatibility (replaced with error), and modify the way to read data + minor details.

Note: complexity and compatibility increased but performance decreased in other to make it more flexible for further changes.

sim = ReadSpice(filename,varargin)

sim is a cell array that contains all simulations: name,
data and labels. Like: sim{i} = [name data labels]. For
extracting data use:
name=sim{i}(1,1);name=name{1};
data=sim{i}(1,2);data=data{1};
labels=sim{i}(1,3:end);
where i can take values from 1 to length(sim)
name (to view the simulation name given by ngspice)
data (to view the numerical data)
labels (to view how the data is labeled)

This script has been tested on raw (-r out.raw) data from
ngspice-rework18.

Usage example:
sim = ReadNGSpice('out.raw');
sim = ReadNGSpice('out.raw','version','18');
name=sim{1}(1,1);name=name{1};
data=sim{1}(1,2);data=data{1};
labels=sim{1}(1,3:end);
plot(data(1,:), data(6,:));
title(name);
ylabel(labels{6});
xlabel(labels{1});