ARROW-5174: [Go] implement Stringer for DataTypes

[sbinet]

No description provided.

[sbinet]

needs #4160

[codecov-io]

Codecov Report

Merging #4161 into master will decrease coverage by 27.35%.
The diff coverage is 26.08%.

@@             Coverage Diff             @@
##           master    #4161       +/-   ##
===========================================
- Coverage   87.89%   60.53%   -27.36%     
===========================================
  Files         758       67      -691     
  Lines       92163     4974    -87189     
  Branches     1251        0     -1251     
===========================================
- Hits        81006     3011    -77995     
+ Misses      11040     1847     -9193     
+ Partials      117      116        -1

Impacted Files	Coverage Δ
go/arrow/ipc/file_reader.go	0% <0%> (ø)	⬆️
go/arrow/array/list.go	74.56% <0%> (-12.18%)	⬇️
go/arrow/ipc/metadata.go	0% <0%> (ø)	⬆️
go/arrow/datatype_binary.go	0% <0%> (ø)	⬆️
go/arrow/array/struct.go	84.31% <100%> (+11.67%)	⬆️
go/arrow/datatype_nested.go	75% <16.66%> (-19.74%)	⬇️
go/arrow/datatype_fixedwidth.go	22.72% <25%> (-8.53%)	⬇️
go/arrow/datatype_numeric.gen.go	37.5% <37.5%> (-12.5%)	⬇️
go/arrow/datatype_null.go	66.66% <66.66%> (-33.34%)	⬇️
go/arrow/array/fixedsize_binary.go	73.8% <79.16%> (+5.38%)	⬆️
... and 706 more

---

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 1c0930d...e6ec020. Read the comment docs.

[sbinet]

PTAL @stuartcarnie @alexandreyc @nickpoorman

[sbinet]

(the Travis-CI error is unrelated (JDK-9 is acting up?))

[alexandreyc]

LGTM

(except for arrow-cat and arrow-main that I did not fully review since I need read the whole thing first :))

[sbinet]

thanks.

feel free to comment on the PR(s) that I might have already collected and I'll retrofit those comments.

[stuartcarnie]

💯