Changes for version 1.31
- Add 3 new methods: getSiblingCount(), isFirstChild() and isLastChild(). Warning: getSiblingCount() does not include the invocant, unlike getAllSiblings().
- Add t/24_Tree_Simple_sibling_test.t.
- These methods are used by Tree::Simple::View::HTML V 0.19 to output HTML compatible with the HTML5 standard for nested lists. See https://www.w3.org/wiki/HTML_lists#Nesting_lists. Thanx to Ekkehard Plicht for suggesting this, and for the patches, which I have reworked. See RT#121099.