This is a fix and small improvements release

Fix display of uplink messages
add -A option to display only downlink messages
add -g gain option to set rtl dongle preamp gain
add -p ppm to set ppm frequency correction for rtl dongle
improve -o 0 output (now print the beginning of message )
use sse2 optimized vector math lib for AM demod (more than 40% CPU load improvement)
other small performance optimizations

PS :Acarsdec is a multi-channels acars decoder with built-in rtl_sdr front end.