Use hex format for NRF51822 target
Updated exporters to a merge-friendly format
Restore serial_api.c on LPC1768

Michael's GPIO fix changed this to a previous version, this commit restores
it to the last version.
Merge branch 'master' of github.com:mbedmicro/mbed
Merge branch 'master' of https://github.com/mbedmicro/mbed