[rpki] DRL RPKI code moving to GitHub

[Rob Austein]

After ten years of self-hosting with Subversion and Trac, we're moving
the DRL RPKI code (aka "the rpki.net code", "the ISC RPKI code", ...)
to GitHub.

You can find the new repository at:

  https://github.com/dragonresearch/rpki.net

The hope is that this change will make things simpler for users of our
code while reducing amount of time we have to spend on infrastructure
maintenance (our Trac instance, in particular, has not aged well).

We think we've managed a fairly complete migration:

* All code which was in the Subversion repository is now in the git
  repository, including the full history.

* All tickets in the Trac system are now issues in on GitHub (so you
  can search the fully history, including all the closed issues).  The
  conversion here is not perfect: GitHub does not allow us to pretend
  that all of this has been happening on GitHub for the last ten
  years, so some of the meta-data for the uploaded issues reflects
  what happened while uploading rather than what's been happening in
  Trac for the last ten years -- but there are footnote lines in all
  the converted stuff documenting what the names, dates, and states
  were in the original Trac tickets, so it should be possible to piece
  together the history in the unlikely event that anybody cares.

* All contents of the trac.rpki.net Wiki have been stuffed into the
  git repository as well, with some preliminary attempts at automated
  conversion from Trac Wiki syntax to GitHub-flavored-Markdown.  At
  some point we may stuff some of this into the GitHub Wiki, but for
  present purposes GitHub's automatic rendering of Markdown source
  files makes this unnecessary.

The old Trac and Subversion instances should be considered read-only,
effective immediately.  We'll leave the old Trac and Subversion
instances available for a little while longer, but will eventually
shut them down or replace them with pointers to the stuff on GitHub.

Other changes which are happening at the same time as all this:

* The code which was the Subversion "trunk" is now the "old-trunk" in
  the git repository.   We stopped all development on this code a
  while ago, and at this point it's unlikely that we'll ever touch it
  again except perhaps for critical security vulnerabilities -- and
  even then, perhaps not, as it depends on old versions of external
  packages which may themselves have unfixed vulnerabilities.

  We have also disabled automated package builds for this branch.

* The git "master" branch in git is what we've been calling the
  "development" branch in Subversion, where it had the silly name
  "tk705".  This is where all the serious development effort has gone
  for several years now; it's smaller, faster, uses current versions
  of the external libraries it needs, runs on database engines other
  than MySQL (these days we prefer PostgreSQL), and supports new
  features like RRDP.

  We are providing packaged builds for this branch, currently only for
  Ubuntu Xenial and Debian Jessie.  See the documentation on GitHub
  for details.

Since all of this is on GitHub, you are of course welcome to fork,
hack, open issues, generate pull requests, whatever.

We will look at issues and pull requests as time permits.  As always,
we make no promises in advance about accepting anybody's code changes,
but we will look at them.