Adds netmask and broadcast address handling.
Broadcast messages are now recognised by packet event handler.
Buffer created by initialize to avoid need to create in parent application.
Enable / disable broadcast and multicast now toggles relevant bits rather than setting all other bits.
Adds enableMulticast function.
Improvements to documentation.
Reverts changes to data buffer.
Merge pull request #114 from riban-bw/master

Subnet and broadcast message handling.