[m-dev.] referenced papers

[Zoltan Somogyi]

In several modules of the compiler and library, and probably other
directories as well, we reference papers that provide the basis for
the module, or are otherwise relevant to its understanding. The
references often include URLs, but these links can go dead.
(This email is motivated by finding one such dead link.)

I think we should add a new directory to the mercury git module
in which we can store our own copies of these papers. We would still
of course say where the paper appeared and what the original URL
we fetched it from was, but a link going dead won't make the paper's
contents inaccessible. By putting the paper on the web, the authors
have implicitly agreed that this is fine for people to do.

Any disagreements? Any preferences as to the name of the new
directory?

Zoltan.