Added .gitignore with some basic ignores.
[software] Added a whole bunch of Python scripts for handling VDIF.

vdif.py:
    Library with Python clases for reading/writing VDIF

vdif_recv.py:
    Script for receiving VDIF packets over 10 GbE.

vdif_check.py, checks.py:
    Script for checking quality of VDIF files.

vdif_corr.py:
    Script for correlating one or more VDIF files.

vdif_sim.py:
    Script for generating simulated VDIF data files.