Version 2.2.0

This feature release improves Go compilation speed somewhat by no longer tracking Go dependencies by default.
The disadvantage of this approach is that ninja will no longer report "nothing to do" when nothing has changed, instead the Go programs will all be recompiled.
Go build has for a while now had a builtin cache however, which means that it's generally fast to re-run it when nothing has changed, thus that ends up being faster than to track dependencies.