Document the functions whitelist option in AbstractFunctionRestrictionsSniff
Document the functions whitelist option in AbstractFunctionRestrictionsSniff

This feature was added in #626, but not properly documented so far.

jrfnl/WordPress-Coding-Standards,mattyrob/WordPress-Coding-Standards,WordPress-Coding-Standards/WordPress-Coding-Standards,WordPress-Coding-Standards/WordPress-Coding-Standards,paulschreiber/WordPress-Coding-Standards,jrfnl/WordPress-Coding-Standards,jrfnl/WordPress-Coding-Standards,jrfnl/WordPress-Coding-Standards,paulschreiber/WordPress-Coding-Standards,mattyrob/WordPress-Coding-Standards,paulschreiber/WordPress-Coding-Standards,WordPress-Coding-Standards/WordPress-Coding-Standards,mattyrob/WordPress-Coding-Standards,paulschreiber/WordPress-Coding-Standards,WordPress-Coding-Standards/WordPress-Coding-Standards,mattyrob/WordPress-Coding-Standards,mattyrob/WordPress-Coding-Standards