--net-beast switch added

Hi, 
Changes I've added are...

1) Implemented a timestamp counter for each received message. The timestamp has a 500nS (2Mhz) granularity.

2) Added a new command line switch, "--net-beast". This causes the output from Dump1090 to be in Beast binary format, containing the 6 byte timestamp data.

3) Tidyied up the code a bit to make it easier for me (A M$ windows native) to understand. That doesn't necesserily mean it'll be easier for you (as a Linux user) to understand :-)

Cheers
Malcolm