py: Fix range to support negative step

[corona10]

Fixes: #41

[codecov-io]

Codecov Report

Merging #42 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
+ Coverage   65.91%   65.95%   +0.04%     
==========================================
  Files          57       57              
  Lines       10206    10208       +2     
==========================================
+ Hits         6727     6733       +6     
+ Misses       3005     3002       -3     
+ Partials      474      473       -1

Impacted Files	Coverage Δ
py/range.go	81.81% <100%> (+6.81%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5e97b9b...d356b20. Read the comment docs.

[corona10]

@ncw Please take a look :)

[ncw]

I think the code looks fine - can you fix the conflict though?

[corona10]

@ncw
Done!
Thanks for the quick review, I hope you had happy Christmas with your family!

[ncw]

That looks great - thanks!

Unfortunately Santa gave me and my whole family Norovirus so I guess we must have been on the naughty list after all! We've recovered now though. I hope your Christmas was better :-)