Add worker config property

Adds a worker config property to allow control over the number of processes that the Tornado will use to serve the application.

Upgrade dependencies

Upgrade Pillow and Tornado to their latest versions. Github was reporting a security vulnerability in version 2.9.0 of Pillow.

Add background to transparent images

Supports adding a background color to a transparent image. Particularly useful when converting from an image type that supports transparency to one that does not. This is a backwards incompatible change. It changes the default background from fff to 0fff. In order to restore the previous behavior, update the config to set background=ffff.

Add TIFF support

Bump version to 1.1.11

Support for TIFF file types

Add ca_certs option

Supports setting the CA certificates