Adds support for blame ignore.

Windows and non-Windows scripts are provided for initial setup.
Commit hashes to ignore are entered in the file .git-blame-ignore-revs

.git-blame-ignore-revs

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+# When making commits that are strictly formatting/style changes, add the
+# commit hash here, so git blame can ignore the change.
+# See docs for more details:
+# https://git-scm.com/docs/git-config#Documentation/git-config.txt-blameignoreRevsFile
+
+# Example entries:
+# <full commit hash>  # initial black-format
+# <full commit hash>  # rename something internal

tools/configure-git-blame-ignore-revs.bat

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+rem Other config options for blame are markUnblamables and markIgnoredLines.
+rem See docs for more details:
+rem https://git-scm.com/docs/git-config#Documentation/git-config.txt-blameignoreRevsFile
+
+rem Uncomment below and rerun script to enable an option.
+rem git config blame.markIgnoredLines
+rem git config blame.markUnblamables
+
+git config blame.ignoreRevsFile .git-blame-ignore-revs
+git config --get blame.ignoreRevsFile

tools/configure-git-blame-ignore-revs.sh

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+# Other config options for blame are markUnblamables and markIgnoredLines.
+# See docs for more details:
+# https://git-scm.com/docs/git-config#Documentation/git-config.txt-blameignoreRevsFile
+
+# Uncomment below and rerun script to enable an option.
+# git config blame.markIgnoredLines
+# git config blame.markUnblamables
+
+git config blame.ignoreRevsFile .git-blame-ignore-revs
+git config --get blame.ignoreRevsFile