Changed the way the functions operate the spectrometer

Now the functions inside **estrella_classes** operates better the spectrometer, hiding some unnecessary stuff from the end user.
After the changes, the user just need to insert the calibration parameters in the new *txt* and run the program. Also, is really easy to implement the async scan after the changes, using the functions **estrella_ascan** and **estrella_aresult**.
Some error handling was added too.