platform/nrf51822/log: Improve buffer length calculation
platform/nrf51822/log: Fix number of parameters of APP_UART_INIT() macro
examples: Add Makefile to build all examples
radio: Add radio_send_then_recv() API
examples: Add adv scannable example
radio: Fix NRF PCNF0 config

In-RAM representation of radio packet, S0, LENGTH, and S1 are optional.
For BTLE radio packet, S1 can be omitted setting its length to zero
(omitting in memory).
example: Fix length field of broadcaster example