Handle expanded values for run option "--doc"

[tbrowder]

Currently the only way to affect pod leading declarator block text handling is with an environment variable.

It would be much more convenient for the user to select that behavior by adding an extra run option "--doc-fmt=" so one could run Raku something like this:

raku --doc --doc-fmt=preserve ...

or

raku --doc=HTML --doc-fmt=preserve ...

[coke]

Is it worth abbreviating as "auth-fmt" instead of using "author-format" or perhaps "original" ?

[tbrowder]

@lizmat and @vrurg have already weighed in on the PR I'm working on. The new PR will use a new option with one argument for the current situation. Example use:

$ raku --doc --doc-fmt=preserve ...

where 'preserve' means "keep original text format in declarator blocks."

@vrurg wants to ensure we retain the flexibility to have new uses handled if need be.

[tbrowder]

A new PR is the way and will cover most of this discussion.