add mode() function & tests

[jsternberg]

No description provided.

[jsternberg]

@agaurav before I merge this, which email do you want to use as the author for this commit? I see @opavader and @agaurav seem to be both you, but with different emails. I want to make sure the commit log has the credit given to the correct GitHub username.

[jsternberg]

@jwilder can I also get a thumbs up that this is OK to merge into 1.0 to be released with the next release candidate?

[agaurav]

@jsternberg I think i signed the CLA with this account (@agaurav), so please use this.

[jsternberg]

Looking at the CLA responses we've gotten, I see you used @agaurav as the GitHub account name, but you used ashish@archsaber.com as the email. That email appears to be linked to your other account. Do you want to use that email with the commit or a different email?

Either one is fine with me.

[agaurav]

Yeah you can use that.

[jwilder]

Looks great @agaurav! This is missing a changelog entry though.

[jwilder]

cc @nathanielc

[agaurav]

@jwilder #7207 for changelog.
Also, influxdata/docs.influxdata.com-ARCHIVE#585 for updating the docs.