Adding inset and margings to plots (new feature in the plot package)

I put up a pull request to the racket plot package to allow controlling the margin left around a plot picture. The motivation for this is that, when using thicker lines for the drawing, the end caps for these lines are cut off at the plot margin and the lines extend past he legend bounding box.

Here is an example with the lines at extreme widths, to make the effect obvious, the problem exists at thinner widths:

The PR adds two new parameters to control the space around the plot and correct this problem:

I'm posting this here, since not many people monitor the plot repository, and I would like some feedback from the community on this PR, including if there is a better approach to fixing this problem. Here is the PR:

Thanks,
Alex.