le: jump to next channel earlier

Jump to the next channel in a hop pattern well in advance of when the
next packet is scheduled to arrive. This should help address issues with
clock desync between Ubertooth and
devices.

The previous behavior was to jump just moments before the next packet
was sched to arrive. If the device clock was slightly slower than
Ubertooth clock, we would jump too late and miss packets.
le: dump packets to PCAP file
le: record packet RSSI and stuff into PPI header

This patch includes a version tag on the PPI header as well to allow for
future enhancements.
le: switch modulation mode to LE in bt_le_generic

This corrects an amazingly bone-headed error wherein we left the device
in BR modulation mode when trying to sniff LE packets. This resulted in
Ubertooth not seeing a majority of packets transmitted by the slave
device.
host: modulation flag for ubertooth-dump
dump: dump LE bitstream as ASCII
host and firmware: utility and command for reading a CC2400 register

This commit adds a new command-line utility (ubertooth-debug) and an
Ubertooth command for reading an aribtrary CC2400 register.
firmware: SPI function for writing multiple bytes to a register

This can be used to write multiple consecutive bytes to the FIFO.
le: transmit
le: get AA properly when it's at the beginning of the DMA buffer
meta: gitignore new ubertooth-debug tool
le: do not verify packets once connection is being followed

CRC calculation is slow, and attempting to filter packets on-device with
the CRC causes us to miss other packets. We do need it set on
advertising channels so we don't accidentally start following a bogus
connect packet.
le: listen on specified advertising channel
le: improve and simplify promiscuous mode

 - search for other types of empty packets
 - automatically jump to a sane channel
 - squelch away the noise
 - reduce number of times we must witness an AA
 - keep a bigger LFU cache of AA's
le: set PCAP length to 128 to prevent packets from getting truncated
le: faux slave mode

Ubertooth will spam advertising packets for a given MAC address. Shows
up on Linux with hcitool lescan.
le: refactor out LE state into its own struct
le: partially working RX with sync detection

first packet received correctly, rest are garbage
Fix typo in firmware version check [thanks to Jonathan Miner]
le: dma one packet at a time