Renamed FES date filtering function

`date_range` and `dateRange` functions renamed to `fes_date_filter`

Fixes #141
We brainstormed a bit yesterday about how to get a normal test suite to fake running each notebook, to at least catch any exceptions.  Then it can be hooked up to Travis-CI, which works extremely well with our always-PR approach.  We'll try to flesh something simple out today for this.