Add buster image

Copy-pasta from stretch, which is a copy of jessie.

debian/buster/Dockerfile

+FROM debian:buster
+
+LABEL maintainer="ethitter"
+LABEL version="1.0"
+
+RUN echo "deb http://security.debian.org/ buster/updates main" >> /etc/apt/sources.list
+
+RUN apt-get update \
+    && apt-get -y --no-install-recommends install \
+        apt-transport-https \
+        lsb-release \
+        ca-certificates \
+        curl \
+        git \
+        dh-make \
+        build-essential \
+        autoconf \
+        autotools-dev \
+        libpcre3 \
+        libpcre3-dev \
+        libz-dev \
+        gnupg \
+        libssl-dev \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/*