retrosheet v1.1.2

• Replaced kludge-y closeAllConnections() with close() calls to specific connections (#1)
• Added some rudimentary data cleanup to the get_retrosheet() wrapper function
  • Dates in retrosheet data now return date-types, everything else is converted from chr via the relatively aggressive type.convert()
• Removed data.table dependency, replaced data.table::fread() with base::read.csv() calls
• get_retrosheet() now returns regular old dataframes now, instead of tibbles.
• Added better handling of HTTP requests. Failed requests are now retried up to three times via httr::RETRY()