Add .gitorder and shell script to use it

Author: opensdh

.gitorder

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+source/std.tex
+source/layout.tex
+source/styles.tex
+source/macros.tex
+source/tables.tex
+source/cover-*.tex
+source/front.tex
+source/intro.tex
+source/lex.tex
+source/basic.tex
+source/expressions.tex
+source/statements.tex
+source/declarations.tex
+source/modules.tex
+source/classes.tex
+source/overloading.tex
+source/templates.tex
+source/exceptions.tex
+source/preprocessor.tex
+source/lib-intro.tex
+source/support.tex
+source/concepts.tex
+source/diagnostics.tex
+source/utilities.tex
+source/strings.tex
+source/containers.tex
+source/iterators.tex
+source/ranges.tex
+source/algorithms.tex
+source/numerics.tex
+source/time.tex
+source/locales.tex
+source/iostreams.tex
+source/regex.tex
+source/atomics.tex
+source/threads.tex
+source/grammar.tex
+source/limits.tex
+source/compatibility.tex
+source/future.tex
+source/back.tex
+source/xrefdelta.tex

tools/gitconfig.sh

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+#!/bin/sh
+git config diff.orderFile .gitorder