Keep order of children

In the final figure, the order of children of a node does not necessarily be as specified in the grammar.

Add an option to keep the order.

changed milestone to %0.3.6

assigned to @rschoene

created merge request !4 (merged) to address this issue

mentioned in merge request !4 (merged)

mentioned in commit f8512ae0

closed with merge request !4 (merged)

mentioned in commit 8e910ed0