zmwangx and jgm make_spec.lua: fix migration of children nodes in create_anchors (#536)
* make_spec.lua: rename children to child

Naming a variable "children" when it holds one child is confusing, and blocks
naming actual children.

* make_spec.lua: fix migration of children nodes in create_anchors

Prior to this commit, when migrating the children of a node to a new one,
children are moved as they are iterated via `cmark_node_next`; however, when a
child is moved under the new node, its next relationship with its sibling is
broken, so in fact at most one child is migrated, and the rest are lost. This
resulted in cases like

    [Decimal numeric character
    references](@)
    consist of...

(note the softbreak) being eventually rendered as

    <a ...>Decimal numeric character</a>
    consist of...
Latest commit 5dc2aed Oct 5, 2018