No standard utf8 string library is scary - I would happily learn all the mem gymnastics to make this work but fiddling with competing UTF8 libraries as is the case with C/C++ is just not my cuppa.
Well, there's functions for working with code points within the bytes that (may) make up utf8 strings.. in order to do actual string level manipulation a library is needed (such as https://github.com/jecolon/ziglyph or others)
