include status on graph

[schettino72]

Show which tasks are up-to-date or not.

[gaulinmp]

I wrote up a preliminary solution to showing status via color: https://github.com/gaulinmp/doit-graph/tree/uptodate-status.

The salient code:

uptodate_colors = {
    None: {'color':'chocolate4'},
    'up-to-date': {'color':'springgreen3'},
    'run': {'color':'firebrick1'},
    'ignore': {'color':'grey'},
}
# ...
def _execute(self, subtasks, reverse, horizontal, uptodate_status, outfile, pos_args=None):
#...
    if (uptodate_status):
        # Add the node attributes from the dictionary: uptodate_colors[status]
        # Using the **dict syntax allows for multiple attributes to be set at once
        status = self.dep_manager.get_status(task, self.tasks).status
        node_attrs.update(uptodate_colors[status])

If this looks acceptable, I can submit a pull request.