Stop using deprecated API tokens for Enterprise.

Authentication by API token is deprecated and doesn't work anymore.
Instead, authentication should be done via OAuth token now.
Declare the exception type.
Update constructor to use OAuth tokens rather than API tokens.
Remove apiToken completely.
Merge branch 'pull-33'
Cleaned up the authentication part of the code
if the user name is available, pass that in and save a lookup
In fact there's no point in looking up the 'token' property since API token is no longer supported by GitHub
added a little helper code that generates an OAuth token for ~/.github
Formatting only changes
doc improvement