Feature request: Select case for abbreviations

[retodomax]

I would find it useful if it would be possible to convert to snake case but keep abbreviations capital letters, e.g. an additional argument which determines the capitalization of the abbreviation

snakecase::to_snake_case("Mass Flow CO2", abbreviations = "CO2")
#> mass_flow_co2
snakecase::to_snake_case("Mass Flow CO2", abbreviations = "CO2", abbreviation_case = "uppercase")
#> mass_flow_CO2

Thanks for the package!

[chihyunkim]

I would like to add my support for this request.

I especially would appreciate the ability to render abbreviations as uppercase when converting to Sentence case, which is intended for human readability like Title Case (which already has this behavior).