Feature Request: Add DisableFormat option

[TheLartians]

Hey thanks for this great project!

When running cmake-format on a grepped list of files it could be useful to provide a disable-format config option, which can be used to disable formatting completely inside a directory. This would enable us to use cmake-format in a similar automated manner as clang-format, which provides such an option.

I've briefly searched through the docs and couldn't find any equivalent option.