Guide: added tcsh setenv syntax in addition to bash
I have answered a question from a user who couldn't
get "export" command to work on her Mac OS X, and
then I realized that since some time, default shell on
Mac OS X is tcsh which has a different syntax.
Get rid of globals in getgraph by packaging vars in a struct.  Resolves issue #62.
Merge branch 'develop' into iss64-other-conventions