Windows performance is terrible?

I use Macs. So to test MultiMarkdown on Windows, I have to use a virtual machine (I use UTM with Windows 11 - ARM 64).

I have finally gotten `ctest` to work on Windows (and on GitHub with Windows VMs), which shows an order of magnitude or so performance hit on windows.

For example, running the `mmd-7` test takes around 0.30 seconds on my machines, but around 8 seconds on a Windows VM. It takes roughly 3.5 seconds on the GitHub Windows VM (and under 0.20 seconds on Ubuntu VM).

Obviously there are multiple factors at play, but even allowing for performance issues due to running on a VM, it seems that something is slow within MultiMarkdown itself.

It's been enough of a PITA getting Visual Studio Code and CMake working on Windows -- trying to get a proper debugger and time-profiler working on Windows is probably not worth the effort.

But if anyone uses Windows, and wants to help improve the performance of MultiMarkdown on Windows, I am open to collaborating!

Thanks