Adds a `create_benchmark` script that automates the following three tasks:
1. Add a new Swift file (YourTestNameHere.swift), built according to the template below, to the {{single-source}}directory.
2. Add the filename of the new Swift file to CMakeLists.txt
3. Edit main.swift. Import and register your new Swift module.
The process of adding new benchmarks is now automated and a lot less error-prone.