Update Golang image for Buster

See merge request !17

Add dependencies for building Debian packages

See merge request !16

Restore WP.org plugin image as a submodule

See merge request !15

Remove WP.org plugin-deploy image

See merge request !14

Slim down Debian images

See merge request !13

Introduce slim image for WP.org plugin deploys

See merge request !12

PHP: add rsync

See merge request !11

PHP: add git to all images; Go: update golint path

See merge request !10

PHP: add git to all images; Go: update golint path

See merge request !9

See https://github.com/golang/lint/commit/ead987a65e5c7e053cf9633f9eac1f734f6b4fe3

Its presence is reasonable alongside subversion.

Add buster image

See merge request !8

These were included in a misguided attempt to fix the nginx build process, which was failing due to OpenSSL not supporting parallel make jobs.

This is purely copy-pasta from the Stretch build.

Add Stretch

See merge request !7

THis is purely copy-pasta from the Jessie build.

Add Debian Jessie build image

See merge request !6

https://github.com/koalaman/shellcheck/issues/1069

Automated image builds for registry

Closes #2, #3, and #1

See merge request !5