chore: add eigen library for vector math

thirdparty/eigen.lua

@@ -0,0 +1,23 @@
+eigen = {}
+
+function eigen:include(includes)
+	if includes:handle(self:name()) then
+		includedirs {
+			path.join(ThirdPartyFolder(), "eigen", "Eigen")
+		}
+	end
+end
+
+function eigen:link()
+end
+
+function eigen:use()
+	
+end
+
+function eigen:name()
+    return "eigen"
+end
+
+function eigen:project()
+end