HackStudio: Show documentation preview in tooltip on identifier hover

When hovering over a C++ token that we have a man page for, we now show
the man page in a tooltip window.

This feels rather bulky at the moment, but the basic mechanism is quite
neat and just needs a bunch of tuning.

Base/home/anon/little/main.cpp

@@ -4,5 +4,6 @@ int main(int, char**)
 {
     // This is a comment :^)
     printf("Hello friends!\n");
+    mkdir("/tmp/xyz", 0755);
     return 0;
 }