Issues/64 - registered_delivery should default to 0b00000001 (#72)

What:
- make `registered_delivery` default to `0b00000001`

Why:
- SMPP v3.4 supports 3 different types of delivery confirmations:
  (i) SMSC Delivery Receipt (bits 1 and 0)
  (ii) SME originated Acknowledgement (bits 3 and 2)
  (iii) Intermediate Notification (bit 5)

  Before this PR, the default used to be 0b00000101 which meant
  we are trying to combine type (i) and type (ii) of delivery confirmation:
      1. SMSC Delivery Receipt requested where final delivery outcome is delivery success or failure. - type (i)
      2. SME Delivery Acknowledgement requested - type (ii) 
  
  With the new default of 0b00000001 we are only using type (i);
      1. SMSC Delivery Receipt requested where final delivery outcome is delivery success or failure. - type (i)

- closes: #64

naz/client.py

@@ -54,7 +54,7 @@ def __init__(
         # xxxx01xx SME Delivery Acknowledgement requested
         # xxx0xxxx No Intermediate notification requested
         # all other values reserved
-        registered_delivery=0b00000101,  # see section 5.2.17
+        registered_delivery=0b00000001,  # see section 5.2.17
         replace_if_present_flag=0x00000000,
         sm_default_msg_id=0x00000000,
         enquire_link_interval=300,