Add analogReference function to switch between default VDD/4 reference and internal reference for ADC.#1876

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stuthedew:develop

Commits on Jul 30, 2019

Added ability to change ADC voltage reference
stuthedew
committed

Commits on Aug 3, 2019

Commits on Aug 10, 2019

Added conditional declarations for analogReference so non-nrf boards will compile
stuthedew
committed