To test lastest BLE_API and nRF51822 with mbed SDK, change the path of these libraries in CMakeLists.txt.
# define some more paths to projects we depend on
set (MBED_SRC_PATH ${BLUE_SOURCE_DIR}/../mbed/libraries/mbed)
set (BLE_API_SRC_PATH ${BLUE_SOURCE_DIR}/../BLE_API)
set (NRF51822_SRC_PATH ${BLUE_SOURCE_DIR}/../nRF51822)