adds julia set example (#419)

* adds julia set example

* fixes indentation in *.js files

* fixes *.js formatting

* fixes a typo in function arguments signature

examples/julia_set/index.js

@@ -0,0 +1,17 @@
+import('./julia_set')
+    .then(wasm => {
+        const canvas = document.getElementById('drawing');
+        const ctx = canvas.getContext('2d');
+        
+        const realInput = document.getElementById('real');
+        const imaginaryInput = document.getElementById('imaginary');
+        const renderBtn = document.getElementById('render');
+
+        renderBtn.addEventListener('click', () => {
+            const real = parseFloat(realInput.value) || 0;
+            const imaginary = parseFloat(imaginaryInput.value) || 0;
+            wasm.draw(ctx, 600, 600, real, imaginary);
+        });
+        
+        wasm.draw(ctx, 600, 600, -0.15, 0.65);
+    });