Support formatting .csproj files and other types of xml

[belav]

It could use the same indent and EOL settings.
Not sure about width, it could always not line break for now.
It would be nice for keeping csproj files consistent, I did that on a work project that was ~190 files and it was a pain, and things still get inconsistent.

[belav]

Implementing #288 should be part of this, so that you can pipe file types besides .cs