Add propane and initial scene grammar

src/sceneparser.propane

@@ -0,0 +1,22 @@
+<<
+import std.conv;
+>>
+
+token background;
+token comma /,/;
+token number /\d+(\.\d+)?/;
+token lt /</;
+token gt />/;
+token semicolon /;/;
+
+Start -> Statements;
+
+Statements -> ;
+
+Statements -> Statement Statements;
+
+Statement -> BackgroundStatement;
+
+BackgroundStatement -> background Vec3 semicolon;
+
+Vec3 -> lt number comma number comma number gt;