Write errors to STDERR
credulous source username@account_alias works

We need to add some error handing and generally tidy
this up.
Add a deploy component so that Travis can upload packages to GitHub
Pass errors back when checking account and username
Permit force saving of credentials without validating username@account (Issue #20)
Emit warning message when force-saving (Issue #20)
Added bash_completion [issue #34]

$ credulous source m[TAB]
mbailey@mbailey            mike.bailey@non-prod-corp
Added bash_completion to README.md
First cut at generating a CHANGELOG using gitchangelog

Happy to switch to a better one if anyone feels strongly.
I've not used this one but thought the output looked OK.
We need to prune it.
credulous source example.user@example-account-alias
Tidy up Usage messages