Speech bubbles deserve corners

[austin3dickey]

Hi @jayqi ,

Thanks for this package; it's really helped me advance in my work.

I think Spongebob's speech bubbles deserve to look a bit nicer with corners. This wikipedia page points out some great ASCII characters that can create nice-looking ASCII boxes. I've used some in slaph.

[jayqi]

These look like Unicode characters. I think this should still work fine, but I'd like to do some more testing/research to understand them and make sure they print as expected. In particular, when will UTF-8 printing fail?

I think some of the other stuff I have generally could be improved with Unicode as well.