Add easing example app, restructure dirs a little

src/textual/cli/cli.py

@@ -172,6 +172,14 @@ def run_app(import_name: str, dev: bool, press: str) -> None:
 @run.command("borders")
 def borders():
     """Explore the border styles available in Textual."""
-    from ..devtools import borders
+    from textual.cli.previews import borders
 
     borders.app.run()
+
+
+@run.command("easing")
+def easing():
+    """Explore the animation easing functions available in Textual."""
+    from textual.cli.previews import easing
+
+    easing.app.run()

src/textual/cli/previews/easing.css

@@ -0,0 +1,8 @@
+EasingButtons > Button {
+    width: 100%;
+}
+EasingButtons {
+    dock: left;
+    width: 20;
+    overflow: auto auto;
+}

src/textual/cli/previews/easing.py

@@ -0,0 +1,22 @@
+from textual._easing import EASING
+from textual.app import ComposeResult, App
+from textual.widget import Widget
+from textual.widgets import Button, Static
+
+
+class EasingButtons(Widget):
+    def compose(self) -> ComposeResult:
+        for easing in EASING:
+            yield Button(easing)
+
+
+class EasingApp(App):
+    def compose(self) -> ComposeResult:
+        yield EasingButtons()
+        self.text = Static("Easing examples")
+        yield self.text
+
+
+app = EasingApp(css_path="easing.css", watch_css=True)
+if __name__ == "__main__":
+    app.run()