Provide a GetString to get string type instead of byte slice

[goodspark]

Could we get a function to just return the string type instead of a byte slice?

I often just need the string and noticed GetStringByte is actually converting the underlying string to a byte.

func (v *Value) GetString(keys ...string) string {
  v = v.Get(keys...)
  if v == nil || v.Type() != TypeString {
    return ""
  }
  return v.s
}

[Aliaksandr Valialkin]

This won't work, since v.s is backed by byte slice, which changes on the next Parser.Parse call. This means that the returned string contents will become garbage on the next Parser.Parse call.