ARROW-3964: [Go] Refactor examples of csv reader
ARROW-3964: [Go] Refactor examples of csv reader

Example of godoc doesn't include input file(testdata/simple.csv). So it's hard to understand the output. This PR refactors it.

<img width="652" alt="screenshot" src="https://user-images.githubusercontent.com/5564044/49687567-0f6fc380-fb48-11e8-895a-ee0d554ef7c8.png">

https://godoc.org/github.com/apache/arrow/go/arrow/csv

Author: c-bata <contact@c-bata.link>

Closes #3131 from c-bata/refactor-csv-reader-example and squashes the following commits:

eed8e29b <c-bata> Refactor examples of csv reader for Go

itaiin/arrow,majetideepak/arrow,majetideepak/arrow,tebeka/arrow,kou/arrow,pcmoritz/arrow,cpcloud/arrow,wesm/arrow,renesugar/arrow,laurentgo/arrow,icexelloss/arrow,laurentgo/arrow,cpcloud/arrow,wesm/arrow,wesm/arrow,icexelloss/arrow,kou/arrow,itaiin/arrow,majetideepak/arrow,laurentgo/arrow,itaiin/arrow,tebeka/arrow,majetideepak/arrow,cpcloud/arrow,laurentgo/arrow,kou/arrow,itaiin/arrow,laurentgo/arrow,cpcloud/arrow,pcmoritz/arrow,tebeka/arrow,pcmoritz/arrow,laurentgo/arrow,laurentgo/arrow,xhochy/arrow,wesm/arrow,apache/arrow,renesugar/arrow,pcmoritz/arrow,pcmoritz/arrow,wesm/arrow,majetideepak/arrow,renesugar/arrow,renesugar/arrow,tebeka/arrow,itaiin/arrow,renesugar/arrow,majetideepak/arrow,kou/arrow,icexelloss/arrow,renesugar/arrow,itaiin/arrow,kou/arrow,laurentgo/arrow,apache/arrow,cpcloud/arrow,itaiin/arrow,xhochy/arrow,pcmoritz/arrow,tebeka/arrow,apache/arrow,icexelloss/arrow,icexelloss/arrow,cpcloud/arrow,wesm/arrow,cpcloud/arrow,apache/arrow,tebeka/arrow,xhochy/arrow,renesugar/arrow,icexelloss/arrow,cpcloud/arrow,apache/arrow,xhochy/arrow,kou/arrow,pcmoritz/arrow,laurentgo/arrow,xhochy/arrow,renesugar/arrow,itaiin/arrow,itaiin/arrow,renesugar/arrow,itaiin/arrow,renesugar/arrow,apache/arrow,xhochy/arrow,apache/arrow,majetideepak/arrow,apache/arrow,renesugar/arrow,laurentgo/arrow,cpcloud/arrow,itaiin/arrow,kou/arrow,wesm/arrow,icexelloss/arrow,pcmoritz/arrow,tebeka/arrow,pcmoritz/arrow,kou/arrow,laurentgo/arrow,xhochy/arrow,icexelloss/arrow,itaiin/arrow,cpcloud/arrow,pcmoritz/arrow,majetideepak/arrow,laurentgo/arrow,kou/arrow,pcmoritz/arrow,majetideepak/arrow,apache/arrow,majetideepak/arrow,icexelloss/arrow,xhochy/arrow,xhochy/arrow,icexelloss/arrow,wesm/arrow,cpcloud/arrow,apache/arrow,tebeka/arrow,tebeka/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,xhochy/arrow,kou/arrow,pcmoritz/arrow,icexelloss/arrow,xhochy/arrow,icexelloss/arrow,majetideepak/arrow,cpcloud/arrow,xhochy/arrow,renesugar/arrow,apache/arrow,itaiin/arrow,wesm/arrow,tebeka/arrow,xhochy/arrow,laurentgo/arrow,itaiin/arrow,majetideepak/arrow,cpcloud/arrow,pcmoritz/arrow,renesugar/arrow,wesm/arrow,apache/arrow,majetideepak/arrow,kou/arrow,icexelloss/arrow,renesugar/arrow,majetideepak/arrow,kou/arrow,wesm/arrow,kou/arrow,pcmoritz/arrow,itaiin/arrow,xhochy/arrow,xhochy/arrow,apache/arrow,pcmoritz/arrow,laurentgo/arrow,renesugar/arrow,apache/arrow,cpcloud/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,majetideepak/arrow