## Named & Default Arguments (#3)

Implement a `joinComments()` function which takes a `String` parameter
containing comment text. `joinComments()` joins the lines of the comment text,
removing newlines and using a default of `;` as the line separator. It removes
the comment slashes along with any whitespace after the slashes (`// `).

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Use the extension function `lines()` to split a `String` into a list of
lines.

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