Add functions: `str_to_pascal()`, `str_to_camel()`, `str_to_kebab()`, `str_to_snake()`

[librill]

Added 4 functions for common programming use. Closes #573 .

All functions call an existing str_to_*() so locale argument respects the behavior of those functions

Aliases StrToPascal() and strToCamel() exist (str-to-kebab() is not a valid name)

[librill]

CC: @kbodwin

[hadley]

Sorry for missing this. Are you still interested in finishing it off? No problems if not, as I'm happy to do it myself.

[kbodwin]

We're happy to make changes if needed! But I'm not sure I see what's missing - do you see something more you'd want for this to be ready for review?