Different comment styles for .c/.h and .cc files

Hello,

I've noticed that `addlicense` generates different comment styles for C/C++ header and source files. Specifically, `.cc` files receive a `//` style header, while `.c` and `.h` files get a `/* ... */` style header.

I'm wondering if this is the intended behavior or a potential bug?

This inconsistency can be problematic for projects that have a strict coding style and require a uniform comment style across all files.

Could you please clarify if this is the intended behavior? If so, would you consider adding an option to configure the comment style for different file extensions?

Thank you for your time and for this useful tool!

Start by locating addlicense's handling for .c, .h, and .cc files and compare how each comment style is selected. Confirm whether the difference is intentional, then define the configuration behavior needed for projects that require a uniform style and verify it across those extensions.

Written by the indexing model from the issue text.