Format a string and push it onto the end of the array. This is a
convenience wrapper combining `strbuf_addf` and `argv_array_push`.
+`argv_array_pop`::
+ Remove the final element from the array. If there are no
+ elements in the array, do nothing.
+
`argv_array_clear`::
Free all memory associated with the array and return it to the
initial, empty state.