[PROPOSED] Replace mscgen with mscgenjs-cli

[barthel]

As part of asciidoctor/docker-asciidoctor#51 I have been trying to create a multi-platform Asciidoctor Docker image.

In doing so,mscgen (https://www.mcternan.me.uk//mscgen/) was a challenge, as there is only one glibc platform or static linked variant and not suitable for Alpine on arm platforms.

To remove this limitation, I looked at mscgenjs-cli (https://github.com/mscgenjs/mscgenjs-cli) and included it.
Since it supports compatible (and more) CLI parameters, replacing the executable was enough.

To further promote platform independence, I would like to propose an official switch to or support of mscgenjs-cli.

mscgen:

Usage: mscgen -T <type> [-o <file>] [-i] <infile>
       mscgen -l

Where:
 -T <type>   Specifies the output file type, which maybe one of 'png', 'eps',
             'svg' or 'ismap'
 -i <infile> The file from which to read input.  If omitted or specified as
              '-', input will be read from stdin.  The '-i' flag maybe
              omitted if <infile> is specified as the last option on the
              command line.
 -o <file>   Write output to the named file.  This option must be specified if 
              input is taken from stdin, otherwise the output filename
              defaults to <infile>.<type>.  This may also be specified as '-'
              to write output directly to stdout.
 -p          Print parsed msc output (for parser debug).
 -l          Display program licence and exit.

Mscgen version 0.20, Copyright (C) 2010 Michael C McTernan,
                                        Michael.McTernan.2001@cs.bris.ac.uk
Mscgen comes with ABSOLUTELY NO WARRANTY.  This is free software, and you are
welcome to redistribute it under certain conditions; type `mscgen -l' for
details.

PNG rendering by libgd, www.libgd.org

mscgenjs-cli:

Usage: mscgen_js [options] [infile]

Options:
  -T --output-type <type>          svg|png|jpeg|mscgen|msgenny|xu|json|ast|dot|doxygen
  -I --input-type <type>           mscgen|msgenny|xu|json|ast
  -i --input-from <file>           File to read from. use - for stdin.
  -o --output-to <file>            File to write to. use - for stdout.
  -p --parser-output               Print parsed msc output
  -s --css <string>                Additional styles to use. Experimental
  -n --named-style <style>         basic|lazy|classic|noentityboxes
  -m --mirror-entities             Repeat the entities on the chart's
                                   bottom
  -v --vertical-alignment <align>  Vertical alignment of labels on regular
                                   arcs. Experimental
                                   above|middle|below (default: "middle")
  --puppeteer-options <file>       (advanced) pass puppeteer launch options
                                   see README.md for details
  -l --license                     Display license and exit
  -V, --version                    output the version number
  -h, --help                       display help for command

[barthel]

WDYT? @pepijnve @mojavelinux

[barthel]

Used and testable via Docker Image https://hub.docker.com/r/uwebarthel/asciidoctor/

Github project (Dockerfile): https://github.com/barthel/docker-asciidoctor