[0.16]

  * Added xml renderer (XML representation of the CommonMark AST,
    which is described in `CommonMark.dtd`).
  * Reduced size of gperf entity table (Nick Wellnhofer).
  * Reworked iterators to allow deletion of nodes during iteration
    (Nick Wellnhofer).
  * Optimized `S_is_leaf`.
  * Added `cmark_iter_reset` to iterator API.
  * Added `cmark_consolidate_text_nodes` to API to combine adjacent
    text nodes.
  * Added `CMARK_OPT_NORMALIZE` to options (this combines adjacent
    text nodes).
  * Added `--normalize` option to command-line program.
  * Improved regex for HTML comments in inline parsing.
  * Python is no longer required for a basic build from the
    repository.