combining size and repeat eos 
In my model coff_symbol type object is not fixed size as it may include optional 'aux' record. So my intention was to create a substream of known size and read from it as many entries as fits this block. But 'size' in this context defines size of stream for every symbol entry not symbols stream size. 

I believe when size and repeat: eos defined in the same scope size should be applied to scope stream and not create substream of size size for every repetition.  As far as I understand this will be inline with size declaration semantics.

```
instances:
  symbols:
    pos: coff_hdr.pointer_to_symbol_table
    size: coff_hdr.number_of_symbols * 18
    type: coff_symbol
    repeat: eos
```

generated code:
```
  _pos = self._io.pos()
  self._io.seek(self.coff_hdr.pointer_to_symbol_table)
  while not self._io.is_eof():
       self._raw__m_symbols_.append(self._io.read_bytes((self.coff_hdr.number_of_symbols * 18)))
       io = KaitaiStream(BytesIO(self._raw__m_symbols_[-1]))
       self._m_symbols_.append(self._root.CoffSymbol(io, self, self._root))
       ...
```

