dedupe 0.5 compatibility and features

Adds compatibility with [dedupe 0.5](https://github.com/open-city/dedupe/pull/172) and adds the following functionality to `csvdedupe`:

* adds `--destructive` flag to `csvdedupe` - output file will only contain unique records
* creates new `csvlink` command for finding matches between two separate CSV files, similar to a SQL `JOIN` statement