ask for `cstr_append_fmt`, `cstr_replace_all`, `cstr_split`

[Liigo Zhuang]

ask for `cstr_append_fmt`, `cstr_replace_all`, `cstr_split`

[Tyge Løvset]

Good suggestions.
Added cstr_assign_fmt(&s, "%s%d", s.str, 100); which works as append_fmt() would.
Added csview_first_token(), csview_next_token() in csview.h, which does split see example.
Added cstr_replace_all()

[Liigo Zhuang]

Thank you! Nice work! ❤