Factor out decorating children.
Factor out creating a fragment span.

Currying this so that I can use it in a later refactor.
Factor out creating the span marker for a fragment
Helper function for surrounding with a fragment.
Curried function for prefixing a fragment.
Specify decorators as function chains.
Rearrange functions.
Decorate double asterisks.
Decorate headers.
Include markdown type in markup fragments.
Decorate links.