Use the build system “meson” (close #32)

Replace the build system “setuptools” with “meson”.

src/main.py

@@ -0,0 +1,11 @@
+import sys
+import gi
+gi.require_version('Gtk', '3.0')
+
+from .application import Application
+
+
+
+def main(version):
+    app = Application()
+    return app.run(sys.argv)