Feature for just running the code without benchmarking

[gaurav-arya]

BenchmarkTools.jl has some special syntax for string interpolation, plus the setup block, etc.

Often I'm @btime'ing something and then I just decide to run it once and simply remove the @btime, but this of course errors, and I need to revise it back to a version that doesn't use any special syntax. As a convenience, it would be nice to have a macro like @runonce which just runs the function once and gives the output, but accepts the special syntax.