the keyword :. [aka :|.|, the one created by (intern "." :keyword)]
can now be used to "splice" a plist into the plist given to the
function returned by DJULA:COMPILE-TEMPLATE

so in `djula' terms

   (funcall template :a 1 :b 2 :c 3 :d 4 :e 5)

can also be written as

   (funcall template :a 1 :. '(:b 2 c 3) :d 4 :e 5)

and in `cl-terrace' terms

   (render "/template.html" :a 1 :b 2 :c 3 :d 4 :e 5)

can now be written as

   (let ((defaults1 (list :b 2 :c 3))
          (defaults2 (list :d 4 :e 5)))
     (render "/template.html" :a 1 :. defaults1 :. defaults2))