ll: Draft for connection initiating state (no Connection state yet)
stack: Add Random number generation API
nrf51822/random: implement random API using RNG peripheral
ll: Fix interval timer callback in initiating state
ll: implemented data channel map & index selection for connection states
Clean: formatting
ll: Add connection context structure
ll: Fix connection parameters to use BLE spec units
ll: Modify initiating function timings to use us instead of ms
ll: distinguish between CONNECTION_MASTER and CONNECTION_SLAVE states
ll: Add CONNECT_REQ PDU struct and initialization functions for PDU and connection context
ll: Completed actions to reply the CONNECT_REQ PDU in initiating state
ll: Initialize connection events counter to 0xFFFF so that the 1st CE sets it to 0
ll: add ll_pdu_data struct for Data packets
ll: central role - timers handling when going from Initiating to Connection state
ll: in ll_on_radio_rx(), rename rcvd_pdu by rcvd_adv_pdu to allow data PDUs as well
ll: in CONNECTION_MASTER state, start connection events by sending Empty PDUs
ll: in connection state, handle supervision timeout
ll: implement ack/flow control mechanism and centralize outgoing packets preparation
nrf51822/radio: add debug option to visualize RX & TX timings on a GPIO pin