codified 0.3.0

• Vignette mimics calling REDCap. (#9)
• Small modernizations. (#9)

codified 0.2.0

• added table_nih_enrollment() and table_nih_enrollment_pretty(). #2
• added nih-enrollment-html vignette. #6
• started pkgdown site. #7
• the idea was created by Peter Higgins (@higgi13425) for R/Medicine 2018.