Allow per-language outline settings

[NorthboundTrain]

I tried to override my default outline.showStrings setting for just one language:

    "[markdown]": {
        "outline.showsStrings": true
    }

and I see the error:

"This setting does not support per-language configuration."

Having strings shown in the outline for a programming language file (e.g. Perl) is a nightmare of noise, but not seeing them for the Markdown language means I don't see my headings listed in the outline. Allowing per-language settings would give the best of both worlds.

[NorthboundTrain]

I had a typo in my variable name -- sorry for the noise!