mbed library sources. Supersedes mbed-src.

Dependents:   Nucleo_Hello_Encoder BLE_iBeaconScan AM1805_DEMO DISCO-F429ZI_ExportTemplate1 ... more

add code to handle rx error of serial in serial_api.c for stm32f3

add code to clear rx error of serial in serial_api.c for stm32f3

mbed library sources. Supersedes mbed-src.