Add new command for generating executableTarget and source boilerplate for new benchmarks

Something like

swift package benchmark init MyBenchmark

creates the Benchmarks/MyBenchmark directory
creates the Benchmarks/MyBenchmark/MyBenchmark.swift source file with the boilerplate:

import Benchmark
import Foundation

let benchmarks = {
    Benchmark.defaultConfiguration = .init(scalingFactor: .kilo)

    Benchmark("SomeBenchmark") { benchmark in
        for _ in benchmark.scaledIterations {
            blackHole(Date()) // replace this line with your own benchmark
        }
    }
}

generates this to standard out (preferably so we can pipe it to pbcopy) :

        // MyBenchmark benchmark target
        .executableTarget(
            name: "MyBenchmark",
            dependencies: [
                .product(name: "Benchmark", package: "package-benchmark"),
                .product(name: "BenchmarkPlugin", package: "package-benchmark"),
            ],
            path: "Benchmarks/MyBenchmark"
        ),

Which can then just be copy-pasted into Package.swift and we're ready to go

ordo-one / package-benchmark

Add new command for generating executableTarget and source boilerplate for new benchmarks #129