`type` field allows use the array syntax for defining type
The following `.ksy` is accepted by compiler (at least in web-IDE) and parses 1 byte:
```yaml
meta:
  id: type_reference_bugs
types:
  u2be:
    seq:
      - id: value
        size: 1
seq:
  - id: value
    type: u2be[]
```
I think, that such constructions should be prohibited. The `seq.type` field should not allow using the "array" syntax for defining a type reference. This not only have unclear semantics, but also threated as a reference to a user type `u2be`.

Another problem that may be misleading is the ability to have a custom type named as one of the built-in. I think we should prohibit this too. In the example above, if you delete the `[]` part from the type, built-in type will be used.