refactor(lib): rename main to __main__ (#82)

* refactor(lib): rename `main` to `__main__`

This allows to call the module using `python -m manim-slides`, useful for profiling, etc.

* fix(setup): update name

manim_slides/__main__.py

@@ -0,0 +1,29 @@
+import click
+from click_default_group import DefaultGroup
+
+from . import __version__
+from .convert import convert
+from .present import list_scenes, present
+from .wizard import init, wizard
+
+
+@click.group(cls=DefaultGroup, default="present", default_if_no_args=True)
+@click.version_option(__version__, "-v", "--version")
+@click.help_option("-h", "--help")
+def cli() -> None:
+    """
+    Manim Slides command-line utilities.
+
+    If no command is specified, defaults to `present`.
+    """
+    pass
+
+
+cli.add_command(convert)
+cli.add_command(init)
+cli.add_command(list_scenes)
+cli.add_command(present)
+cli.add_command(wizard)
+
+if __name__ == "__main__":
+    cli()