Move wiki pages into place

This was accomplished by

  git mv *.png static/img/

and

   git ls-tree --format='%(path)' HEAD^{/^Merge.*wiki}^2 |
   while read path
   do
     test "z$path" != "z${path%.md}" &&
     test -f "$path" ||
     continue

     title="$(echo "${path%.md}" | tr '-' ' ')"

     filename="$(echo "$title" |
       tr 'A-Z' 'a-z' |
       sed 's/[^0-9A-Za-z_]\+/-/g').md"

     sed -i '1i---\ntitle: "'"$title"'"\naliases:\n  - "'"${path%.md}"'"\n---' "$path" &&
     git mv "$path" content/"$filename"
   done

One outlier was `Windows-vs-Linux-fork()/exec()-semantics.md`, which had
to be moved manually.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho