Appendix title overflows page

[mariusbarth]

Hi @dan-weiss

Thank you so much for this wonderful package! Today I ran into a problem that I think is a bug that might be easy to fix (but I'm not an expert in writing LaTeX macros).

With a rather long appendix title, the title overflows the page margins, as can be seen here:

I suspect this might come from using \centerline here, which seems to suppress auto-wrapping. I thought maybe using \centering instead might already solve this issue.

Hope this issue is informative enough that it is easy to fix this issue. If you need any further information, feel free to ask.

Best regards, Marius