easier way to logout

[dandanxu]

instead of having to type solvebio.cli.auth.logout('')
just typing: logout
should log the user out

[rocky]

The branch feature/add-sample-annotation-via-rest-client now adds something similar.

I've added logout(), whoami(), and login() functions. Note that because this is a real Python shell, entering in the shell a simple login will just return the Python method object.

We could do something like ipython does and add `%' in the front so that you can enter %login instead of login().

What do you think?

Also, right now, one might think that the login function would allow user name and password parameters as is the case in the Ruby client. That's not done yet either.

[davecap]

Side note: you can type solvebio logout from your shell and it'll log you out, just not within the "solvebio IPython shell".

[rocky]

This has been added to version 1.6.0. If this is acceptable, please close the issue.