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Add RedBearLab nRF51822 link

Add RedBearLab BLE Nano link

from
https://github.com/ARMmbed/nrf51-sdk/blob/master/source/nordic_sdk/compo
nents/drivers_nrf/delay/nrf_delay.h

Minor update to #12.

Tweaks to #12

Update README.md for first use case

was downloading version 2.0.1 of the soft device but the board definition had 2.0.0 which resolves issue #13

link was to the preview release not the current dk, both link to the same file for now

an extra step for the first out of box experience required for nrf52, took me a few hours to test why the following did not work:
```
void setup() {
  pinMode(PIN_LED1, OUTPUT);
  pinMode(PIN_LED2, OUTPUT);
  pinMode(PIN_LED3, OUTPUT);
  pinMode(PIN_LED4, OUTPUT);
}

void loop() {
  digitalWrite(PIN_LED1, HIGH);
  delay(50);
  digitalWrite(PIN_LED2, HIGH);
  delay(50);
  digitalWrite(PIN_LED3, HIGH);
  delay(50);
  digitalWrite(PIN_LED4, HIGH);
  delay(50);
  digitalWrite(PIN_LED1, LOW);
  delay(50);
  digitalWrite(PIN_LED2, LOW);
  delay(50);
  digitalWrite(PIN_LED3, LOW);
  delay(50);
  digitalWrite(PIN_LED4, LOW);
  delay(50);
}
```

Add tools credits

Add flashing a SoftDevice section

Also, split nRF51 and nRF52 Wire.cpp