double vert notation

Sorry about the huge diff, I didn't realize all the changes in indentation would show up, too --
please dont Ripley me, I'm almost a github virgin..

The only real changes are in `utilities.R` in functions

- `findbars()`
- `subbars()`
- `nobars()`.

That
```modterm <- as.formula(paste("~", gsub("`", "", deparse(expandDoubleVerts(term)))))```
part is admittedly very ugly, but I just couldn't find a way to make it more appealing...