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.

2019/.gitignore

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

2019/adamovsky/.gitignore

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

2019/burton/.gitignore

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

2019/ciura/.gitignore

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

2019/diels-grabsch1/.gitignore

@@ -1,5 +1,5 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
 *.dSYM
 dg1.Z
 guidelines2.txt

2019/diels-grabsch2/.gitignore

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

2019/dogon/.gitignore

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

2019/duble/.gitignore

@@ -1,12 +1,12 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
+*.dSYM
 Darwin
 Darwin.alt
 FreeBSD
 FreeBSD.alt
 Linux
 Linux.alt
-*.dSYM
 indent
 indent.c
 indent.o

2019/endoh/.gitignore

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

2019/giles/.gitignore

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

2019/karns/.gitignore

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

2019/lynn/.gitignore

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

2019/mills/.gitignore

@@ -1,11 +1,11 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
+*.dSYM
 Eugene_Onegin.txt
 IOCCC-Rules-Guidelines.txt
 IOCCC-hints.output.txt
 IOCCC-hints.txt
 Shakespeare.txt
-*.dSYM
 gru1
 gru2
 gru3

2019/poikola/.gitignore

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

2019/yang/.gitignore

@@ -1,23 +1,23 @@
 #
-# sort with: sort -d -u
+# sort with: ../../bin/sgi
+*.dSYM
 a
 b
 c
 d
-*.dSYM
 e
 indent
 indent.c
 indent.o
 input.txt
 original.txt
-output.txt
 output1.txt
 output2.txt
+output.txt
 prog
 prog.orig
-scrambled.txt
 scrambled1.txt
 scrambled2.txt
 scrambled3.txt
+scrambled.txt
 unscrambled.txt