flac(1) man page should refer to multiple -A functions as semicolon-separated, not comma-separated

[mjb2010]

flac.md has two references to apodization functions needing to be "comma-separated", whereas I believe the text should say "semicolon-separated". Commas don't work.

The same change will be needed on the web version, if it's not automatic.

[H2Swine]

Consider it "in the works" - I have started a more comprehensive rewrite of the help text, see the links just added. The fact that commas don't work (at least noe in every locale) escaped me, so the proposed draft is insufficient, but hopefully this error should be fixed in the end too.