Add more vops with hex representation to list in account history API docs

enum_virtual_ops method description update (account history API). Added more vops to list with their hex representation. List of newly added vops:

• dhf_funding_operation
• dhf_conversion_operation
• expired_account_notification_operation
• changed_recovery_account_operation
• transfer_to_vesting_completed_operation
• pow_reward_operation
• vesting_shares_split_operation
• account_created_operation
• fill_collateralized_convert_request_operation
• system_warning_operation,
• fill_recurrent_transfer_operation
• failed_recurrent_transfer_operation
• limit_order_cancelled_operation,
• producer_missed_operation
• proposal_fee_operation
• collateralized_convert_immediate_conversion_operation
• escrow_approved_operation
• escrow_rejected_operation
• proxy_cleared_operation