We already have a LICENSE file that covers the Zig Standard Library. We
no longer need to remind everyone that the license is MIT in every single
file.
Previously this was introduced to clarify the situation for a fork of
Zig that made Zig's LICENSE file harder to find, and replaced it with
their own license that required annual payments to their company.
However that fork now appears to be dead. So there is no need to
reinforce the copyright notice in every single file.
Remove the constants that assume a base unit in favor of explicit
x_per_y constants.
nanosecond calendar timestamps now use i128 for the type. This affects
fs.File.Stat, std.time.nanoTimestamp, and fs.File.updateTimes.
calendar timestamps are now signed, because the value can be less than
the epoch (the user can set their computer time to whatever they wish).
implement std.os.clock_gettime for Windows when clock id is
CLOCK_CALENDAR.
