Major revision, now includes the beginnings of an html library.  May be buggy.
* esxml.el: Many new docstrings, replaced type-assert with cl.el's
  check-type.  Added esxml-head which includes a simple DSL for
  tersely specifying the head element of an html document.
Modified esxml-listify to allow specifying item attributes.
* esxml.el: (esxml-listify) now has additional optional argument item-attrs
Switched from destructuring-bind to pcase-let.
* esxml.el: bug fixes and initial transition to pcase.