Allow users to pass Trello token via environment variables

[remolueoend]

Dear Michael, first of all thank you very much for developing and maintaining this project!

I'd like to ask you if you are interested in a PR for allowing users to pass their Trello token via environment variables. This would allow them to load their credentials from an external credential store, such as GNU pass or any other password manager, and forward them to trello-cli.

Conveniently, trello-cli makes use of the package nconf for reading configuration values, which has an additional API for loading values from environment variables too (unfortunately I had to upgrade the package to make use of it).

I "hacked" a patch together which works, but needs quite some cleanup. But before I start with that, I wanted to ask you about your opinion first.

Thanks and kind regards, remolueoend

[mheap]

Hey @remolueoend, I love the idea!

I believe that common convention is that environment variables are in upper case, so it should be TRELLO_CLI_ as a prefix, but otherwise I'd love to see this implemented and merged 👍

[remolueoend]

Hey @mheap, sorry for not pushing anything the last few month, got stuck with a few other things. I already did a cleanup, but there's still some work left regarding testing. I may have to refactor the nconf stubbing which is currently persisted across tests. I hope I can push something working in the coming weeks.

[mheap]

Closing as #162 adds this functionality in v1.0.0 (not yet available)

[remolueoend]

Hey Michael, nice that the feature finally landed :)