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.

1990/.gitignore

@@ -1,2 +1,2 @@
 #
-# sort with: sort -d -u
+# sort with: ../bin/sgi

1990/baruch/.gitignore

@@ -1,9 +1,9 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
+*.dSYM
 baruch
 baruch.alt
 baruch.orig
-*.dSYM
 indent
 indent.c
 indent.o

1990/cmills/.gitignore

@@ -1,8 +1,8 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
+*.dSYM
 cmills
 cmills.orig
-*.dSYM
 indent
 indent.c
 indent.o

1990/dds/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 dds
 dds.orig

1990/dg/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 dg
 dg.orig

1990/jaw/.gitignore

@@ -1,7 +1,7 @@
 #
-# sort with: sort -d -u
-atob
+# sort with: ../../bin/sgi
 *.dSYM
+atob
 indent
 indent.c
 indent.o

1990/pjr/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 indent
 indent.c

1990/scjones/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 indent
 indent.c

1990/stig/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 indent
 indent.c

1990/tbr/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 indent
 indent.c

1990/theorem/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 fibonacci
 fibonacci.c

1990/westley/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 indent
 indent.c