Hello org-mode users,

Here's a patch that adds the ability to specify :html-head as a function. I think this is a logical change because:

1. It provides a wider range of options for how to use :html-head (before :html-head could only be a string, now it can also be a function.)

2. It is consistent with the behavior of :html-preamble and :html-postamble, which can both either be a string or a function.

I probably did this wrong but anyway here's my attempt at a patch submission. Please let me know if you need any additional information or have any questions.

Thanks,

-Nate