matlab: suggests for enhancements

[mzechmeister]

A number of suggestions to enhance the matlab version. Most of them are inspired by the python version.

• [ ] include an example (evt. with a plot)
• [x] rename glsper_4github to gls
• [ ] automatic creation of the frequency grid (fmin, fmax, ofac keywords)
• [ ] unify the if/else branch (setting w=1)
• [ ] mean could be replaced by dot (requires 1d vectors)
• [ ] fast option for trigonometric recurrences
• [x] center the times t with tmin
• [ ] remove coswt_tau

[mzechmeister]

Closed accidentially.