Add region parameter, screen only output option, command wrapper, bug fixes, v0.7.5
* Add optional region parameter which enables use with GovCloud
* Add screen only output for cases where the credentials may need to be copied to another locaiton for use
* Add command wrapper allowing keyman to execute another command for you with the AWS credential env vars provided to the command
* Fix crash in case where ~/.config or a specified config file path does not exist
* Minor code improvements
* Fix user input to trim leading and trailing whitespace
* Version bump to 0.7.5