python 2.7/3.5 compatible

[meresmclr]

• Fixed a long-standing bug in the original code for SV32 along with the reading speedup of order 2x
• basic demo plotting of a few SV characteristics
• please use revision dced076 or newer, as that's where the long-standing reading bug was fixed for SV32.
• made Python 2.7/3.4 compatible

[fnoble]

Hi @scienceopen, thanks for the patch! I'll try to make time to review and test it more thoroughly at the weekend but I noticed you are submitting the rinexnav.py file under GPLv3. Would you consider submitting under LGPLv3 instead to match the rest of the project?

Thanks,
Fergus

[meresmclr]

Hello Fergus, I made the LGPL update, thanks for noticing

[Fourgot]

How does one politely /bump this PR?

[meresmclr]

@akubiak here https://github.com/scienceopen/pyrinex

[scivision]

I would consider using https://pypi.org/project/pyrinex/ which has vastly more features, speed and is robustly tested and updated frequently