Method find_first_not_of

include/jwt/string_view.hpp:313–316

  size_type find_first_not_of(CharT ch, size_type pos) const noexcept;

  size_type find_first_not_of(basic_string_view str, size_type pos = 0) const noexcept
  {
    return find_first_not_of(str.data(), pos, str.length());
  }

  size_type find_first_not_of(const CharT* str, size_type pos = 0) const noexcept
  {