Add ability to set envvars from the cli

[adoublef]

trafficstars

I created a simple subcommand for setting environment variables from the CLI tool. There are a fair different ways that variables can be added but I've chosen one for now. If setting variables from a file would be of interest or setting via a prompt I am happy to alter

[CLAassistant]

All committers have signed the CLA.

[adoublef]

Came across an issue #138 that also adds the ability to load from a file. I think this could be added with this PR potentially.

[adoublef]

Have been away from this for a while, wondering if this is still something I can continue or shall close.

thanks