Add burst read/write in W5100S.h for using dma.

Modify wizchip_clrinterrupt() to set Sn_IR for clearing SIR.

It is not compatable to W5100.
It is only valid on W5500

Added a break to remove compiler warning.

Compiler warned that there was no break at the end of the case statement. Added the break.

add multicast example

Fix regression KEEPALIVEAUTO Not supported in W5100, W5200

Update dns.c

Fix MQTTClient unaligned access on ARM when using -Os

modify comparing DHCP server ip addres

QoS value was an enum and this value was passed to MQTTSerialize_subscribe as an (int*).
So when -Os optimization is used the QoS enum was set to byte and placed at odd address.
But when the code reached MQTTSerialize_subscribe and the address of pointer to byte was casted to pointer to integer the LDR instruction caused HardFaul because of unaligned int access.

Fixed by forcing to pass char so now it should not matter which compiler is used.

Modify getxxx function 
 - setSn_PROTOR , getSn_FRAGR, setSn_FRAGR
 - Modify the bit of IR register definition

 - Sn_PROTO
Modify getSn_FRAGR,setSn_FRAGR
Modify the bit of IR register definition

Fixed an issue where ping ip address failed after pinging domain name failed.

fix w5100s bug

fix w5100s bit define bugs

1.For W5100S,The array size is one byte smaller

Fixed issue 69

2.W5100S also support KA