Suppress warning messages in circular_overlap

[qdread]

This issue was mentioned by @yyue-r in an email.

One or more of the circular overlap functions currently print warning messages because we don't supply any of the options to as.circular. We need to either supply them as hard-coded options within the function, or provide the user with the options.

[qdread]

I think commit dce56e1 resolves this. I noticed a bug in the code where the function creates the acirc and bcirc objects but never uses them. I fixed that and also cleaned up the function a little bit, and some of the documentation that goes along with it.