[O] emphasis is hard-coded in org-element

[Jonas Bernoulli]

Handling of emphasized text is hard-coded in org-element.el. 

Unfortunaly fixing this requires more than teaching
`org-element-text-markup-successor' about `org-emphasis-alist' because
separate `org-element-TYPE-{parser,interpreter} functions are used for
each type of emphasized text.

Wouldn't it be better if bold, underline, ... would all use the same
parser and interpreter?  I don't see another option that would allow
custom emphasize styles to be used with org-element.

  Thanks,
  Jonas