builtin: Implement enumerate feature

[corona10]

Now, gpython supports enumerate feature

[codecov-io]

Codecov Report

Merging #43 into master will increase coverage by 0.3%.
The diff coverage is 72.22%.

@@ Coverage Diff @@## master #43 +/- ##
=========================================
+ Coverage 65.24% 65.55% +0.3% 
=========================================
Files 56 57 +1 Lines 10150 10186 +36 =========================================
+ Hits 6622 6677 +55 + Misses 3066 3040 -26 - Partials 462 469 +7

Impacted Files	Coverage Δ
builtin/builtin.go	78.72% <100%> (+0.05%)	⬆️
py/enumerate.go	71.42% <71.42%> (ø)
py/arithmetic.go	61.69% <0%> (+1.11%)	⬆️
py/function.go	25.95% <0%> (+1.52%)	⬆️
py/tuple.go	24.52% <0%> (+2.83%)	⬆️
py/list.go	11.83% <0%> (+2.95%)	⬆️
py/sequence.go	23.65% <0%> (+3.22%)	⬆️
py/iterator.go	73.33% <0%> (+73.33%)	⬆️

---

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 f7ea0a4...afd9be0. Read the comment docs.

[corona10]

@ncw PTAL

[ncw]

That looks great :-)

I didn't know enumerate took another parameter!

[corona10]

@ncw
It's the funniest part of this work!

[ncw]

@ncw
It's the funniest part of this work!

Indeed, learning lots of arcane things about python!