[Restructuring] Switch to the Visual Studio 2017 compiler

I really want to drop XP support. We don't have one huge issue with it, but we have a bunch of smaller ones.

No HTTPS support. This one is quite big, but we will probably fix it anyway in #106.
Support dropped in VS2019. But we can still use the VS2017 compiler, which isn't that old, and that can be installed as a VS2019 component, without installing all of VS2017.
Broken _thread support in DLLs. Which means every time we need a thread-local variable, we need to use the TLS functions and deal with these slot things and even today I'm not sure how they work.
No FileOpenDialog. Which means we need two version of the folder picking function, an XP version and a Vista+ version.
Can we use C#/WPF on XP?
And probably a few more things I forgot.

But I suppose using a 2 years old compiler isn't a good enough reason to drop XP support, so I guess we'll postpone the issue to the next time we have something that doesn't work on XP.

So, for now, switch to the VS2017 compiler. To ship the runtime, we can either shove all the DLLs in the binaries/ directory, or run the runtime installer from the wrappers if needed. I lean towards the 2nd one, it seems more clean. But the 1st one doesn't require administrator rights, while the 2nd one probably does...

thpatch / thcrap

[Restructuring] Switch to the Visual Studio 2017 compiler #107