Date handling

[curtisalexander]

How to handle SAS dates

[curtisalexander]

Partially implemented with #39 but will definitely require more work.

[curtisalexander]

Next steps

• Implement methodology to handle a SAS time
• Implement all date, datetime, and time formats
  • https://documentation.sas.com/?cdcId=pgmsascdc&cdcVersion=9.4_3.5&docsetId=leforinforref&docsetTarget=n0p2fmevfgj470n17h4k9f27qjag.htm&locale=en
• Testing!