`book::primitives`: Add `{i, u}128
The following **primitive types** are available:
| type hint | name |
-| :------------------- | :---------------------------------- |
+| :----------------------- | :---------------------------------- |
| `=bool` | boolean |
-| `={i,u}{8,16,32,64}` | standard integer types |
+| `={i,u}{8,16,32,64,128}` | standard integer types |
| `=f{32, 64}` | 32-bit / 64-bit floating point type |
| `=[u8; N]` | byte array |
| `=[u8]` | byte slice |
