add tool to sort .gitignore content

We sort with lines starting with # first.
We sort with lines starting with * second.
We sort with lines that do not start with [#!*] third.
We sort with lines starting with ! fourth.

Example usage in vim with a keyboard macro <escape>f:

```vim
:map ^[f 1G!G../../bin/sgi^M
```

 or via .vimrc:

```vimrc
" sort the entire .gitignore file using ../../bin/sgi
:map  ^[f 1G!G../../bin/sgi^M
```

 NOTE: The ^[ above is ((Escape)) and ^M is ((Control-M)).

Example usage in shell:

```sh
rm -f t && ../../bin/sgi < .gitignore > t && mv -f t .gitignore
```

Suggested usage:

```sh
bin/all-run.sh bin/sort.gitignore -v 1
```

Sorted all winner .gitignore according to this method.
Sorted all year level .gitignore according to this method.
Sorted top level .gitignore according to this method.

.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: bin/sgi
 .DS_Store
 /NOTES
 /archive/historic/1984