Merge cmpopts and cmp package?

As a semi-frequent user of the `cmp` package, most of the time I pull up godoc.org reference is to figure out whether a particular useful option is in `cmpopts` or the `cmp` package. Genuinely curious: is there a meaningful end-user benefit to keeping these packages separate? I seldom use `cmp` without `cmpopts`, and I suspect this is common.

/cc @dsnet