add documentation and golint

[pallavJha]

• Fixes Add the code comments, documetation and golint #16

[eatonphil]

Thanks! This is going to conflict with a PR I have in progress (#15). So I'll commit to this branch after I merge that PR.

I don't find it very useful to have comments that are no more explanative than the struct or function name (e.g. SelectStatement, statementKind, etc.) so I will remove those. But other than that there are some good additions here.

[eatonphil]

I see now that golint requires all these to be documented. In that case, fine.

[eatonphil]

Ok, after looking into things a little bit more I decided to go with just golangci-lint for now which is a little more configurable and I've used it in the past.

Some of these comments could still be useful, but I'd leave that up to you.

If you'd like to get the PR approved I'd say:

1. Drop the golint
2. Remove any comments that are super obvious

Thanks for the effort!

[pallavJha]

Hi @eatonphil

I've removed the golint and tested with the golangci-lint after resolving conflicts and merging with the master.
I've also removed some of the comments that I had added for just because of golint.
You can review it once again.

[eatonphil]

Made a few changes but looks good. Thank you!