Fix NRF51822 PWM and Serial:
- imlement pwmout_free()
- check UART interrupt type carefully
- implement serial_set_flow_control()
- add serial_clear() stub
[NUCLEO_F091RC] pin_mode for Serial only if the pin is present

Same as all other targets.
Merge pull request #538 from bcostm/master

HAL: NUCLEO_F091RC - pin_mode for Serial only if the pin is present
Merge pull request #537 from xiongyihui/stm32f407

HAL: DISC_F407VG, ARCH_MAX - change default toolchain

- ARCH_MAX - use different PeriheralNames.h files
[NUCLEO_F030R8] port HAL to support cube and ad cube files as well
Merge pull request #541 from dbestm/master

HAL: NUCLEO_F030R8 - port HAL to support Cube and cube files addition
Merge pull request #534 from anpilog/master

HAL: nrf51822 - Few fixes for PWM and Serial
[NUCLEO_F401RE] enhance gcc ld file
Merge pull request #543 from dbestm/master

CMSIS: NUCLEO_F401RE - ARM GCC ld RAM size correction
[HAL][ARCH_MAX] add pin names - D14 and D15
README.md add boards of Seeed Arch series