py: Implement range M__getitem__

[corona10]

Fixes: #46

[codecov-io]

Codecov Report

Merging #47 into master will increase coverage by 0.01%.
The diff coverage is 73.33%.

@@ Coverage Diff @@## master #47 +/- ##
==========================================
+ Coverage 65.95% 65.96% +0.01% 
==========================================
Files 57 57 Lines 10208 10223 +15 ==========================================
+ Hits 6733 6744 +11 - Misses 3002 3004 +2 - Partials 473 475 +2

Impacted Files	Coverage Δ
py/range.go	80.24% <73.33%> (-1.58%)	⬇️

---

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 c140988...0cf77c6. Read the comment docs.

[corona10]

@ncw PTAL

[ncw]

Looks perfect - well done :-)