Implemented more enemies and a tier system

core/assets/shaders/default.vertex

@@ -0,0 +1,16 @@
+uniform mat4 u_projTrans;
+
+attribute vec4 a_position;
+attribute vec2 a_texCoord0;
+attribute vec4 a_color;
+
+varying vec4 v_color;
+varying vec2 v_texCoord;
+
+uniform vec2 u_viewportInverse;
+
+void main() {
+    gl_Position = u_projTrans * a_position;
+    v_texCoord = a_texCoord0;
+    v_color = a_color;
+}