BREAKING CHANGE: Most of string functions mutates the string instead of copying now.
This allows better performance when copy is not needed.
It also allows more granual control.
If copy is wanted, simply use `string_copy` before calling the function.
Impacted functions are:
`string_to_uppercase`, `string_to_lowercase`, `string_replace`,
`string_trim_start`, `string_trim_end`, `string_trim`,
`string_capitalize`, `string_reverse`