Allow an AWS region to be passed into the library

[jonathankeebler]

I ran into a problem where I was trying to make Athena queries against two AWS regions simultaneously. I was using aws.config.update to set my region each time, but that's a global config that would change in-between the Athena and S3 calls in athena-express.

To solve, I've added a new config parameter region that can be passed into the constructor. If it's not passed, the default behaviour will set the region.

[coveralls]

Pull Request Test Coverage Report for Build 99

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 91:	0.0%
Covered Lines:	6
Relevant Lines:	6

---

💛 - Coveralls

[ghost]

Is there a chance to merge it into the main code as we need the same feature here