Add ability to persist login values

[jacrys]

I'd like to see the ability to persist the login values through either env_vars or a persistence file. I am lazy and hate typing :)

something like:
export JIRA_SITE='http://example.com' export JIRA_PATH='' export JIRA_USERNAME='balderdash' export JIRA_TOKEN='FQQF748595FFWE'

I would just submit a pull request, but I apparently don't know enough ruby to implement something like this.

[MittchoBaroco]

Can I work on this ?

[ghosteathuman]

@MittchoBaroco By all means, go ahead! Looking forward to a PR :)