[Parser] Referencing another class limitations

[polsm91]

I don't think it makes sense to invest time in fixing the parser, we should move to type hints. But to have this documented somewhere:

Referencing another class only works in some circumstances. e.g:

class OtherClass(StorageObj):
  '''
  @ClassField myvar int
  '''


# This will crash

class A(StorageObj):
  '''
  @ClassField OtherClass
  '''

# This will work

class B(StorageObj):
  '''
  @ClassField __main__.OtherClass
  '''

class B(StorageObj):
  '''
  @ClassField /custom/path/file.py:OtherClass
  '''

Also, this is the reason why we need to place class definitions in separate files in PyCOMPSs.