Fix exporters on UBLOX_C027

Temporary solution, until the exporter infrastructure is modified
to support proper target aliasing/inference.
Update Exporter README
Add NRF51822 to exporter readme
[NUCLEO_F302R8] enhance SPI slave
Merge branch 'master' of https://github.com/mbedmicro/mbed
Merge pull request #313 from dbestm/master

 [NUCLEO_F302R8] enhance SPI slave
Bumped revision number
Added LPC11U68 to the official build
Merge branch 'master' of https://github.com/mbedmicro/mbed