Updated netlist_reader.py to use the natsort library for sorting.

[BillyPocketNC]

This may make installing for kicad harder.

I found the natsort library in pip, and changed the file to use it.
Would you like to include this change? I know it could make installing this project more difficult.

This is related to issue #156

[set-soft]

But this should be controlled by an option!

[BillyPocketNC]

Thanks @set-soft. I will put this in my todo list.

[SchrodingersGat]

@BillyPocketNC long time to review on this one, sorry.

If you want to see this merged, please add the library requirement to setup.py (under install_requires section)

Also, please wrap in a try-catch so that it doesn't break for users who don't have natsort installed:

try:
    from natsort import natsorted
    groups = natsorted(groups, ...)
except ImportError:
    groups = sorted(...)