Add tests of quirks about date ranges
arxiv_open: open abstract pages for search results
Simplify test-data_range; I now understand behavior of search with dates

  - Need a range of dates/times, not just a single date/time
  - * doesn't seem to do anything; you just get the same as if you'd
    truncated, which is to use earliest time that matches that part of
    the string.
  - If you want to search all of 2013, you'd use [2013 TO 2014]
  - If you want March, 2013, use [201303 TO 201304]
arxiv_search: use limit arg rather than end

 - this is more like rplos
 - also more convenient
Lazy load the two datasets.
Add submittedDate and lastUpdatedDate to query_prefixes dataset
Fix errors in sortBy and sortOrder param to API
arxiv_open: use delay_if_necessary between calls to browseURL