[test] Added an example songbook with several tests

patacrep/data/examples/example-test.sb

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+{
+"bookoptions" : [
+    "diagram",
+    "repeatchords",
+    "lilypond",
+    "pictures"
+  ],
+"booktype" : "chorded",
+"template" : "patacrep.tex",
+"encoding": "utf8",
+ "content": ["tests/*.sg", "tests/*.sgc"]
+
+}

patacrep/data/examples/songs/tests/nolyrics.sgc

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+{title: No lyrics}
+{subtitle: Test of verses without any lyrics}
+
+[A]This is a [Bb]verse
+With [C#]lyrics
+
+[Adim] [Dmaj]
+[Em3]
+
+[G4]This is [Emaj3]another
+[Absus8]With lyrics