ldeo-glaciology/firn_accumulation_model: finalized after second revisions

Code to run simulations and plot the figures in review here. Instructions on how to run the code can be found in the README file.

This release includes revisions to the figures made in response to reviewer comments as discussed in the open discussion accessible at the link above.

• Increased font size of tick labels and axis labels.
• added dots and a line to figures 3 and 4 to indicate the bubble close-off depth.

It also includes minor changes made after the second round of reviews to make the code compatible with Matlab 2022a.