Update to Singularity/3.5.2-GCC-5.4.0-2.26, fix --use flag

• Update Singularity version to Singularity/3.5.2-GCC-5.4.0-2.26, as previous (Singularity/2.6.1-GCC-5.4.0-2.26) was erroring out on singularity: "docker://ewels/multiqc:dev"

• Also improved syntax message in ./install.sh

• Also fixed a logic problem with --use flag (adds --use-conda and/or --use-singularity, if the directives are present in Snakefile)

Add Singularity support

Upgrade to Snakemake 5.9.1, which has fixes to Singularity support.

Add loading of Singularity module.

Add checking for 'singularity:' directives to snakemakeslurm warning system.

Add '--use' which auto-generates --use-conda and/or --use-singularity when those directives appear in the Snakefile.

use cluster.slurm.cheaha.json

Previous release included a typo which cause it to skip ./cluster.slurm.cheaha.json

this release fixes that (Issue #3), and improves related output for "--debug" mode.

cleanup cluster.slurm.cheaha.json

release 3 - improve commenting and remove unused attributes in cluster.slurm.cheaha.json

• remove un-used and confusing 'cpus-per-task' attribute from default rule resources; replace with documentation on where threads/cpus are actually set, and add documentation for 'ntasks' attribute
• Add %x=job_name to default log name, to match current module code on cheaha; add URL to documentation on SLURM filename_pattern variables: https://slurm.schedmd.com/sbatch.html#lbAH