Updated kramdown converter to accept custom elements
Loading custom kramdown adaptions so that conversion to kramdown works
Added correct category to custom elements
Fixed problem with last element in tree being omitted and empty paragraph elements not being omitted
Updated IDML story parser

* Sub-Title, Song stanza, Song, IDTitle1, IDTitle2 and IDParagraph
  paragraph styles are now recognized

* FillColor="Color/GAP RED" is now recognized

* <Properties> elements are now ignored as sub-elements of
  ParagraphStyleRange and CharacterStyleRange elements