Implementation of the scripting interface for bls_vec

[zonca]

Exactly same arguments of bls_pulse.py, added detrend_order for detrending, 0 means no detrending.

Basically now:

• bls_pulse_vec.py is the library to be used in Python scripts
• bls_pulse_vec_interface.py is the scripting interface to be called from bash

[scfleming]

The relevant changes have been manually merged in v1.1 branch.