Include lint names in slicec[-cs] -A

[bernardnormier]

We currently output:

 -A, --allow <WARNING>
          Instruct the compiler to allow (not emit) the specified warning

It should say which lint name(s) you can pass.

The plain reading of the current description is you can have only one warning after --allow. Is that correct?

[InsertCreativityHere]

Is that correct?

Yes, none of our command line options support passing multiple arguments at once.
They each have to be passed on their own:
-a Deprecated -a DuplicateFile or -D SYMBOL1 -D SYMBOL2

Simply because we couldn't come up with a unambiguous was to support lists.