text/diff: add example for Files, Lines, Text, and Unified

While at it,

- reorganize the order of functions alphabetically, following
  the order from doc.
- changes the [Line.String] to print text in double quoted to help human
  compare the changes for non-printable characters.

2 files changed, 24 insertions, 0 deletions

diff --git a/lib/text/diff/testdata/lao.txt b/lib/text/diff/testdata/lao.txt
new file mode 100644
index 00000000..635ef2c4
--- /dev/null
+++ b/lib/text/diff/testdata/lao.txt
@@ -0,0 +1,11 @@
+The Way that can be told of is not the eternal Way;
+The name that can be named is not the eternal name.
+The Nameless is the origin of Heaven and Earth;
+The Named is the mother of all things.
+Therefore let there always be non-being,
+  so we may see their subtlety,
+And let there always be being,
+  so we may see their outcome.
+The two are the same,
+But after they are produced,
+  they have different names.
diff --git a/lib/text/diff/testdata/tzu.txt b/lib/text/diff/testdata/tzu.txt
new file mode 100644
index 00000000..5af88a8f
--- /dev/null
+++ b/lib/text/diff/testdata/tzu.txt
@@ -0,0 +1,13 @@
+The Nameless is the origin of Heaven and Earth;
+The named is the mother of all things.
+
+Therefore let there always be non-being,
+  so we may see their subtlety,
+And let there always be being,
+  so we may see their outcome.
+The two are the same,
+But after they are produced,
+  they have different names.
+They both may be called deep and profound.
+Deeper and more profound,
+The door of all subtleties!