Move cached server to XDG-compliant location

[milhnl]

Hey, I'm working on integrating this project into my workflow. This seems like a useful first step, as I like to keep my home directory clean. Please take a look at the "roslyn-language-server.github.com" url included in the commit. It's meant to be a project url. I use my own domain for this most of the time, but I did not see a website on your GitHub profile, so this is just a suggestion. I think it is only used in url form on macOS.

[SofusA]

Thanks for working on this. This is great!

In start_roslyn() a log directory is located relative to the home directory.
I think we should use the project directory here as well and remove the dependency to home

[SofusA]

It would make sense to find the project directory in start_roslyn() and add project directory as an argument to ensure_roslyn_is_installed().

[milhnl]

Hi, thanks for the suggestions! I completely missed the log files. I couldn't resist make the path handling immutable, so the commit is a bit bigger than necessary. If you want me to split it, that's possible, but I thought you wouldn't care.

[SofusA]

This is nice 😃

I really appreciate your work.