[Link] Basic link implementation
- enqueue(): add packet to buffers
- transmit(): transmit packets according to their timestamps
- report(): reports flow_rate, buffer_occupancy, packet_drop
Fix typo, packet ts, and report function
[Link] Style and typo fix
Fixed conversion constants
[Link] More style fixes
Merge pull request #17 from kexinrong/Link

[Link] Basic link implementation