Implement automatic batching for points, lines, shapes, and images/quads.

The above are batched together into a single draw call when called without other drawing calls in between, as long as the following criteria are met:

- The texture is the same.
- The primitive type is the same (points cannot be batched with non-points).
- The love.graphics state is the same (aside from the current color - i.e. setColor - and the transform state).
- The active shader’s uniform values are the same.

You can examine the ‘drawcalls’ field of love.graphics.getStats() to help determine if your code is allowing for optimum batching.

--HG--
branch : minor

src/modules/graphics/opengl/Shader.h

@@ -215,6 +215,8 @@ private:
 
 	int getFreeTextureUnits(int count);
 
+	void flushStreamDraws() const;
+
 	// Get any warnings or errors generated only by the shader program object.
 	std::string getProgramWarnings() const;