[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[time] Switch callers of syscalls with timeouts to use conversion function

This is in preparation for moving syscalls to absolute deadlines rather
than relative timeouts.

Change-Id: Ic85abbf76f34fbce7899c2505be840e3d3dcf7ff

[time] Update some code to use new time convenience macros

Change-Id: I6289116690e46948c0f2d39e68939331173335d7

[system] align license and license banners with Fuchsia

This adjusts the Magenta userspace code to match the prevailing
license in Fuchsia (three-clause BSD), using the same banner
and license text.

Change-Id: I6b6d79435c5dbaa32027888874849e4f47aaa7be

[system][utest]/[mxsh] Make runtests output less by default

To output the full amount use "runtests -v".

This introduces a verbosity_level concept for system/ulib/unnittest
with unittest_set_verbosity_level(level) to control it.

Change-Id: I0f301adf4fdac9a3cf6c76e41d4b9587c9495d1f

[syscalls][api] rename _magenta_*() to mx_*()

The _magenta_ prefix is pretty unwieldy.
This change simplifies that a bit.

This was done mechanically, and boots, runs, and passes tests
on qemu arm64, amd64, and NUC.

Change-Id: I8eb07db6ed6f4b8cac96344cc4ad65ce3f85f917

[ulib][unittest] Move unittest into its own library

Change-Id: I1586278e3bbb6ceacd26a1342985922dc8861cf7

[build][userspace] Support .init_array for userspace with gcc

In particular, with this change, C++ constructors are running now, and
static C variables are initialized.

Change-Id: If0252773faae705af78902f782aaa200d0c5f85e

[utest] Port errno test to use test framework

Change-Id: I3955ef0fff9eefc187bf0f4a4c13568cf4f1fe87

[magenta] Initial commit