Feature request: custom list markers

[dsanson]

Extend the syntax for example lists to allow the author to specify the marker instead of letting
it be determined automatically. E.g, something like:

(@=P1). All men are mortal. 
(@=P2). Socrates is a  man. 
(@=C).  Socrates is mortal. 

And then refer back later to premise (@P2). 

would generate something like:

\begin{itemize}
\item[P1]\label{P1}
All men are mortal.
\item[P2]\label{P2}
Socrates is a man.
\item[C]\label{C}
Scorates is mortal.
\end{itemize}

And then refer back later to premise (\ref{P2}). 

For a bit more discussion, including some other suggested syntaxes, see https://groups.google.com/d/msgid/pandoc-discuss/c89be225-fd55-410f-abd3-7c5f2108d061@googlegroups.com?utm_medium=email&utm_source=footer

[brainchild0]

This support would be very useful. Currently, definition lists are supported, the similarity already noted in the mailing list discussion, but have a different desired appearance than that of lists of the kind currently suggested, both in Markdown source and published output.

Since the AST type definitions would be essentially the same in both cases, the DefinitionList type might simply be generalized to something like LabelList, with the stylization difference being resolved separately.