wildbook.flexibleDate() .. ugh, humans and their communications/dates!
bug fix for 1-digit month in flexibleDate(); added possibility of parseDate getting only YYYY or YYYY-MM in
add .dateAsString() to allow YYYY and YYYY-MM [WG-16]
use new enc.dateAsString() and sort numerically [WG-16]
flexibleDate for showing encounter dates [WG-16]