Allow for variables to be fed in instead of using OS environment variables

[Electro707]

As the title says, this library should allow for some information like client-id to be fed into it with the user application instead of using environment variables. Then these variables can be stored in the library's configuration file. The configuration file as well should be given to the library as an argument instead of using an environment variable.

[Electro707]

Started work on this in my branch: https://github.com/Electro707/digikey-api/tree/json_config_storage
So far for V3 it's working. I don't plan on updating the V2 code to handle this tough.
Still needs to have the OAuth API save the tokens to the config file (right now it saves it in a temporary file in /tmp/dk_config) Done, although some more work needs to be done before it can be potentially merged upstream

[eeintech]

I would like to see this too 😃
Can you create a PR?

[Electro707]

Yup, created under #15. Set as a WIP as more things needs to be done before it can be merged upstream, some things up for discussion.