Compress external threads. Saves 4 bytes per ctx switch.

Dropped support for loading context switch data in previous versions of
traces.

server/TracyVersion.hpp

@@ -7,7 +7,7 @@ namespace Version
 {
 enum { Major = 0 };
 enum { Minor = 5 };
-enum { Patch = 5 };
+enum { Patch = 6 };
 }
 }