Split vulkan_base into smaller units

Closes #30. This is a basic refactoring of the graphics module, so
everything won't be in single file.

graphics/shaders/shader.frag

@@ -0,0 +1,8 @@
+#version 450
+
+layout(location = 0) in vec3 fragColor;
+layout(location = 0) out vec4 outColor;
+
+void main() {
+    outColor = vec4(fragColor, 1.0);
+}

graphics/shaders/shader.vert

@@ -0,0 +1,17 @@
+#version 450
+
+layout(binding = 0) uniform UniformBufferObject {
+    mat4 model;
+    mat4 view;
+    mat4 proj;
+} ubo;
+
+layout(location = 0) in vec2 inPosition;
+layout(location = 1) in vec3 inColor;
+
+layout(location = 0) out vec3 fragColor;
+
+void main() {
+    gl_Position = ubo.proj * ubo.view * ubo.model * vec4(inPosition, 0.0, 1.0);
+    fragColor = inColor;
+}