Allow users to disable null method warnings

[pselle]

mark.end(foo) was called from @iopipe/iopipe but this method was not available. You may have called this method outside of an invocation or @iopipe/core needs to be upgraded to satisfy version ^1.11.0
label(bar) was called from @iopipe/iopipe but this method was not available. You may have called this method outside of an invocation or @iopipe/core needs to be upgraded to satisfy version ^1.11.0

When a user is say, unit testing outside of the main invocation, these warnings could be expected/noisy.