[crossfire] Git for arch, maps, server, and client

[Kevin Zheng]

Hi there,

Some months ago I proposed switching the arch, maps, server, and client 
repositories to Git. Since feedback on the mailing list was positive, I 
think now is a good time to make the switch.

- If you have SVN checkouts of the arch, maps, server, or client
   repositories, get Git and clone the Git version from:

   https://sourceforge.net/p/crossfire/_list/git

   If you are running a server that tracks one of these repositories, you
   should probably update those, too.

- Before UTC Saturday 2021-05-08 22:00, please continue committing to
   SVN as usual. I will be manually keeping the Git up to date with SVN,
   so it may be a bit slow keeping up. Please do not commit to Git during
   this time.

- At UTC Saturday 2021-05-08 22:00, I will update these Git repositories
   from SVN one last time. Future commits in these repositories should go
   into Git. SVN will continue to be used for the repositories that
   haven't switched. The migrated repositories will still continue to
   exist in SVN for a while, but should not be committed to. Hopefully
   nobody gets confused by the fact that there are two repositories. At
   some point, perhaps we should delete these repositories from SVN.

I'd like to tentatively suggest this policy for commits going into Git:

1. To preserve linear history, no merge commits in 'master'. When
    merging branches into 'master', rebase the branch against 'master'
    and then do a fast-forward from 'master'.

2. Commit messages begin with a short, one-line summary, followed by a
    blank line, followed by more detailed explanatory text, if necessary.
    Lines are wrapped to approximately 72-ish characters.

Comments and feedback is appreciated, as is your patience while we make 
the switch.

Regards,
Kevin