CRAN Update

Fixes from issues plus minor enhancements to existing functions

• Resolved error reading tables with user and multiselect fields
• Removed data.table dependency
• Changed from snow to parallel for parallelization of JSON encoding (snow superseded by parallel)
• Added type_cast argument to update which enables pushing new multi-select options

CRAN Release

Now available on CRAN (commit 6ab6687)

Initial Release

All elements of an Airtable CRUD workflow have been tested at this point, but it is likely that there are still bugs to be ironed out, documentation improvements to be made, and features to be added.