Add a base dockerfile to only build the xeps in CI

Dockerfile

@@ -1,24 +1,10 @@
-FROM debian:8
-MAINTAINER XSF Editors <editor@xmpp.org>
+FROM xmppxsf/xeps-base:latest
 
-ENV DEBIAN_FRONTEND noninteractive
-
-RUN apt-get update && apt-get -y dist-upgrade
-RUN apt-get install -y xsltproc libxml2-utils libxml2 texlive fonts-inconsolata make nginx
-
-RUN mkdir /src
 COPY *.xml xep.* *.css *.xsl *.js *.xsl Makefile /src/
-RUN mkdir /src/resources
 COPY resources/*.pdf /src/resources/
-WORKDIR /src
-RUN apt-get install -y curl python python-pip texlive-xetex 
-RUN curl https://pilotfiber.dl.sourceforge.net/project/getfo/texml/texml-2.0.2/texml-2.0.2.tar.gz -o texml-2.0.2.tar.gz && tar -xf texml-2.0.2.tar.gz && pip install texml-2.0.2/ && rm -rf texml-2.0.2
-RUN apt-get install -y texlive-fonts-recommended texlive-fonts-extra
-RUN mkdir /var/www/html/extensions
-RUN OUTDIR=/var/www/html/extensions/ make html pdf
 
-RUN cat /sys/fs/cgroup/cpuset/cpuset.cpus || true
-RUN cat /proc/cpuinfo || true
+WORKDIR /src
+RUN OUTDIR=/var/www/html/extensions/ make -j5 html pdf
 
 EXPOSE 80
 

Dockerfile.base

@@ -0,0 +1,17 @@
+FROM debian:8
+MAINTAINER XSF Editors <editor@xmpp.org>
+
+ENV DEBIAN_FRONTEND noninteractive
+
+RUN apt-get update && \
+    apt-get -y dist-upgrade && \
+    apt-get install -y \
+        xsltproc libxml2-utils libxml2 texlive fonts-inconsolata make nginx \
+        curl python python-pip texlive-xetex texlive-fonts-recommended \
+        texlive-fonts-extra
+RUN curl https://pilotfiber.dl.sourceforge.net/project/getfo/texml/texml-2.0.2/texml-2.0.2.tar.gz -o texml-2.0.2.tar.gz && \
+    tar -xf texml-2.0.2.tar.gz && \
+    pip install texml-2.0.2/ && \
+    rm -rf texml-2.0.2
+
+RUN mkdir -p /src/resources /var/www/html/extensions