stage1: Added `zig help` to show usage on stdout

This will make it easier to do things like `zig help | grep something`.

Invalid arguments will now display a short notice for `zig help`
instead of showing the full usage information. This will make it easier
to see the actual error.
7b204649e3Jay Weisskopf committed on 9/26/2018, 2:05:44 AM· committed by Andrew Kelleyparent2e562a5
1 file changedLine totals unavailable