Introduce a flag to prefer `//` over `/*...*/`

[Dentrax]

It would be great to have a non-multiline comment support enabled with a new flag. Multiline comments /*\n*\n*\n*/ takes more lines and makes it harder to read for me. Here is a simple proposal:

$ touch foo.c
$ addlicense -s=only -c Furkan .

Actual: (Multiline comment)

/*
 * Copyright 2022 Furkan
 * SPDX-License-Identifier: Apache-2.0
 */

New flag way: (comment)

// Copyright 2022 Furkan
// SPDX-License-Identifier: Apache-2.0

[willnorris]

I think what I'd really like to do is have a way to specify a config (config file, set of flags, whatever) that can override any default settings of which file extensions are supported, and which commenting style they use. I think there are still some open pull requests for adding file types that I'm not completely convinced should always be updated. But for folks that want it, it should be easy to add that for them.