Added method sub_block_group to support defining an associated group of similar blocks, with unique classes.
Added method sub_block_group to support defining an associated group of
similar blocks, with unique classes.

e.g.

~~~ruby
  sub_block_group :my_ip_group do
    sub_block :ip0, class_name: 'IP0', base_address: 0x000000
    sub_block :ip1, class_name: 'IP1', base_address: 0x000200
    sub_block :ip2, class_name: 'IP2', base_address: 0x000400
    sub_block :ip3, class_name: 'IP3', base_address: 0x000600
  end
~~~
Creates an array referenced by a method called `my_ip_group`
which contains the sub_block instances for `ip0`, `ip1`, `ip2`, `ip3`.

Origen-SDK/origen,Origen-SDK/origen,priyavadan/origen,priyavadan/origen,priyavadan/origen,priyavadan/origen,Origen-SDK/origen,Origen-SDK/origen