Add method to append argparse option to the Command object.

[nzlosh]

When creating a dynamic command plugin that uses the arg_botcmd function, there is no obvious way to pass multiple arguments to the Command object as is the case when using the Decorator pattern with mutiple arguments.

This pull request adds a new method append_args to the Command object which can take arguments and keywords. Below is an example of how this code would be used.

        Help_Command = Command(
            eg_help,
            name="eg_help",
            cmd_type=arg_botcmd,
            cmd_args=("--topic",),
            cmd_kwargs={"dest": "topic", "type": str},
            doc="Provide example help."
        )
        Help_Command.append_args(("--filter",), {"dest": "filter", "type": str})
        Help_Command.append_args(("--limit",), {"dest": "limit", "type": int})
        Help_Command.append_args(("--offset",), {"dest": "offset", "type": int})

        self.create_dynamic_plugin(
            name="Example_Plugin",
            doc="Example.",
            commands=(Help_Command)

[nzlosh]

The test pipeline is failing but it seems to be something unrelated to the code changes I made.

ERROR    errbot.repo_manager:repo_manager.py:167 Could not update from source https://repos.errbot.io/repos.json, keep the index as it is.

repos.errbot.io doesn't resolve from my machine for example.

[gbin]

@nzlosh fixed please retry. Sorry for that.

[sijis]

Rebased to cleanup the PR.

[nzlosh]

Any thoughts on including this PR in the next point release?

[sijis]

Can't see a reason why not.

[nzlosh]

Should I merge master?

[sijis]

@nzlosh This needs a rebase.

[nzlosh]

@sijis There were a few snags rebasing, but everything has been sorted for a merge to master.

[nzlosh]

Will this PR be include for the next release?

[sijis]

I can look to add it