Misc. fixes for README.
Add extended errors for Vodafone MAM-2G.
Add extended commands for Vodafone MAM-2G.
Add extended optional TLVs for Vodafone MAM-2G.

- MAM2G_SP_DATE
- MAM2G_NOTIFY_DEBIT
- MAM2G_NOTIFY
- MAM2G_SC_TIMESTAMP
- MAM2G_VS_RETINFO
- MAM2G_CS_CODE
Add vs_retinfo values for Vodafone MAM-2G (submit_mt and recharge_mt).
Hook MAM2G_SC_TIMESTAMP and MAM2G_VS_RETINFO into deliver_sm PDU.
Add definitions of mandatory parameters for Vodafone MAM-2G.

- MAM2G_PAYER_ADDR_TON
- MAM2G_PAYER_ADDR_NPI
- MAM2G_SP_CLASS
- MAM2G_SP_SERVICE
- MAM2G_NUMBER_OF_MESSAGES
- MAM2G_MESSAGES
- MAM2G_SM_LENGTH
- MAM2G_TRANSACTION_ID
Add definitions of MAM2G_SUBMIT_MT/RESP for Vodafone MAM-2G.
Add definitions of MAM2G_SUBMIT_CARING/RESP for Vodafone MAM-2G.
Add support for MAM2G_SUBMIT_MT and MAM2G_SUBMIT_CARING.
Add note about MAM2G extensions to README.