ISSUE:17 Add Env Arguments and Bump graphicsmagick version to 1.3.35 + esmero/esmero-cantaloupe:4.1.6RC1

[DiegoPino]

See #17

This allows XMX and XMS to be set on a docker-compose file as environment variables

I also pushed a new tag for the container:

esmero/esmero-cantaloupe:4.1.6RC1 that matches this version can be used inmeditally

If someone wants to test, the change in the corresponding part for our archipelago-deployment the docker-compose.yml file is

iiif:
    container_name: esmero-cantaloupe
    image: "esmero/cantaloupe-s3:4.1.6RC1"
    restart: always
    environment:
      XMX: 4g
      XMS: 2g
    ports:
      - "8183:8182"
    networks:
      - host-net
      - esmero-net
    volumes:
      - ${PWD}/persistent/iiifconfig:/etc/cantaloupe
      - ${PWD}/persistent/iiifcache:/var/cache/cantaloupe

In this case giving initial 2 GBytes that can grow until 4Ggbytes. If none provided defaults to 256m initial and 2G max.