Output more of the provided levels when creating breaks

[al-obrien]

Instead of just returning levels based upon the input data, enforce more of the levels based upon the breaks instead

In create_breaks(), don't index just by the out vector, instead have the levels and labels assigned by the break values as an option.

For example:

    if(all_levels) {
      out <-factor(out, levels = 1:length(brk_labels), labels = brk_labels)
    } else {
         ...
    }