v0.3.2

• Use ${NAME?}q/$(NAME?)s syntax to define nullable placeholder.
• As opposed to optional placeholders that defaults to blank, nullable
  placeholders will default to null.
• Useful for defining nullable string or array items.

Example:

jf "[str or bool, %(str)?q %(bool)?s, nullable, %(nullable?)q]" str=true
# ["str or bool","true","nullable",null]