[SP] add Blink2 project, and related libraries.
[SP] isolate function with flag CURRENT_SENSOR and LIQUID_CRYSTAL_DISPLAY.
[SP] add serial1 monitor function with flag SERIAL1_MONITOR.
[SP] add RF24 radio function with flag RF24_TX and RF24_RX.
[SP] add RF24 library for radio function.
Merge branch 'branch_at_playground' into branch_at_home