canu: add singularity files

src/singularity_modules/canu/1.6/build.sh

+#/bin/sh
+sudo singularity build --force bin/canu:1.6.sif src/singularity_modules/canu/1.6/canu.def
+singularity sign bin/canu:1.6.sif

src/singularity_modules/canu/1.6/canu.def

+Bootstrap: docker
+From: ubuntu:18.04
+
+%labels
+MAINTAINER Laurent Modolo
+
+%post
+CANU_VERSION=1.6
+PACKAGES=canu=${CANU_VERSION}*
+
+apt-get update && \
+apt-get install -y --no-install-recommends ${PACKAGES} && \
+apt-get clean
+
+%environment
+export CANU_VERSION=1.6
+
+%runscript
+exec /bin/bash "$@"