Create an abstraction around the retreival of config from env vars

[tim-zwart]

We can have a private function to perform this check and throw errors, might make it more readable when we have more env variables

Originally posted by @DawYeong in #36 (comment)

[tim-zwart]

I wonder if there's an environment variable parsing library for this purpose?

Originally posted by @xujustinj in #36 (comment)

[tim-zwart]

There is one called envalid that seems to do what we want here. There may also be a way to use the 2nd answer of this stackoverflow post.

Originally posted by @tim-zwart in #36 (comment)

[DawYeong]

#49 (comment) is related to this