Add ability to persist login values

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.