Log Message:
textproc/hs-pandoc-types: Update to 1.23

[1.23]
* Remove Null constructor from Block (#91) [API change].
* ToJSONFilter: Add instance for MonadIO (#105, Willem Van Onsem) [API
  change].
* Add `Figure` block constructor (Albert Krewinkel, Aner Lucero, and
  Christian Despres) [API change]. The new Figure block represents a figure
  with attributes, caption, and arbitrary block content.