add ghostscript & imagemagick

• add ghostscript & imagemagick
• update test.sh

upgrade to alpine 3.11.6

• upgrade to alpine 3.11.6

fix readme

• remove "-output-directory"
• update readme with what's inside docker image
• update goss test : create output directory beforehand tests

v20200216 : fix docker hub client api version issue

fix "client version 1.38 is too new. Maximum supported API version is 1.37" in docker hub

v20200215: first official release

First official release \o/

• embed all texlive