Version 0.2.0
------------------------------------------------------------------------------

* `censor` and `squish` gain `only.finite` argument and default to operating
  only on finite values. This is needed for ggplot2, and reflects the use of
  Inf and -Inf as special values.

* `bounds` functions now `force` evaluation of range to avoid bug with S3
  method dispatch inside primitive functions (e.g. `[`)

* Simplified algorithm for `discrete_range` that is robust to
  `stringsAsFactors` global option.  Now, the order of a factor will only be 
  preserved if the full factor is the first object seen, and all subsequent 
  inputs are subsets of the levels of the original factor.

* `scientific` ensures output is always in scientific format and off the
  specified number of significant digits. `comma` ensures output is never in
  scientific format. (Fixes #7)

* Another tweak to `zero_range` to better detect when a range has zero length.
  (Fixes #6)

