Add additional documentation

[mucaho]

Add documentation:

• explain ProtocolListener.handleUnordered better (it's actually unreceived data that gets skipped over, the argument is the first data after the "gap")
• document jnetrobust-samples
• document Packet & MetaData
• rename MetaData to Segment, to be in line with ISO/OSI terminology analogue to Packet, update Wiki
• document non API classes
• explain Config values better and which listener gets called once constraint violated
• explain Protocol empty ack transmission requirement better. Use RTT and packet send rate.
• add pseudocode diagram for using protocol methods
• move javadoc to github pages
• give overview of project in readme file
• provide API overview in wiki
• document that user is required to send ACK immediately with empty transmission, unless he is sending packets at fixed intervals < 100 ms
• inform user that if he uses protocol without retransmission, he should adapt config values to be more aggressive so he is informed a lot quicker about lost/unordered packets -> 16 should be fine