Convenience version of macro to time a whole function

[KristofferC]

TimerOutputs.jl has the following syntax available

@timeit "zone name" f(x) = x
@timeit f(x) = x # implicitly named section `f`

These seem helpful for this package as well. One issue we have had in TimerOutputs is that these macro types mess up the line info a bit: KristofferC/TimerOutputs.jl#77 so we should be careful not to do that. Base has some features like remove_linenums! that might be useful.