A lightweight, standalone VDL Mode 2 message decoder and protocol analyzer.

Features:
* Runs under Linux (tested on: x86, x86-64, Raspberry Pi)
* Supports following SDR hardware:
- RTLSDR (via rtl-sdr library)
- Mirics SDR (via libmirisdr-4)
- reads prerecorded IQ data from file
* Decodes up to 8 VDL2 channels simultaneously
* Outputs messages to standard output or to a file (with optional daily
or hourly file rotation)
* Outputs ACARS messages to PlanePlotter over UDP/IP socket
* Supports message filtering by type or direction (uplink, downlink)
* Outputs decoding statistics using Etsy StatsD protocol