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.

2020/.gitignore

@@ -1,4 +1,4 @@
 #
-# sort with: sort -d -u
+# sort with: ../bin/sgi
 iocccsize
 iocccsize.o

2020/burton/.gitignore

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

2020/carlini/.gitignore

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

2020/endoh1/.gitignore

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

2020/endoh2/.gitignore

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

2020/endoh3/.gitignore

@@ -1,10 +1,10 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
+*.dSYM
 clock
 clock.alt
 clock.alt.c
 clock.c
-*.dSYM
 indent
 indent.c
 indent.o

2020/ferguson1/.gitignore

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

2020/ferguson2/.gitignore

@@ -1,10 +1,10 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
+*.dSYM
 cake.sh
 chocolate-cake.dat
 chocolate-cake.key
 config
-*.dSYM
 indent
 indent.c
 indent.o

2020/giles/.gitignore

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

2020/kurdyukov1/.gitignore

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

2020/kurdyukov2/.gitignore

@@ -1,8 +1,8 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
-*.jpg
 *.gif
+*.jpg
 *.ppm
 indent
 indent.c

2020/kurdyukov3/.gitignore

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

2020/kurdyukov4/.gitignore

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

2020/otterness/.gitignore

@@ -1,12 +1,11 @@
 #
-# Don't sort because of the exclusion of *.mid with the exception
-# of the cvikl.mid and the entertainer.mid.
+# sort with: ../../bin/sgi
 *.dSYM
+*.mid
 indent
 indent.c
 indent.o
 prog
 prog.orig
-*.mid
 !cvikl.mid
 !entertainer.mid

2020/tsoj/.gitignore

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

2020/yang/.gitignore

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