[docs][syscalls] Add TODOs about documenting system call rights

ZX-2399 #comment

Test: no functional change
Change-Id: I1f285c677e2444fcf1d720d7ecbd9f490c303962

[docs] Clarify level-triggered nature of signals

Previously, the docs were unclear if you read them with a pre-conceived
notion that signals were edge-triggered (as "signals" are in POSIX).

Change-Id: I52bbd7eb652002ecd5479926a6fa1c6c677a4985

[rights][syscalls] introduce ZX_RIGHT_WAIT

This right governs the ability to wait_one(), wait_many(),
or wait_async() on an object. Previously ZX_RIGHT_READ
governed this.

Adjusts userspace and test code to include ZX_RIGHT_WAIT in
various zx_handle_duplicate() and zx_handle_replace() calls.

Change-Id: I92ff9f976150d17f81bf4f3d2a36781e37833060

[docs] Fix typo: s/zx_time/zx_time_t/

Change-Id: I973bb4a8904f6e527e64511353dd127e784b00be

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[docs][errors] Rename all the errors in docs/ to MX_OK and MX_ERR_*

Change-Id: I62451456a83145760c6454a619d4c699ce8e9017

[syscalls] Switch all syscall interfaces to deadlines

Change-Id: If1c2540b7aa3d16e8080551100b19fb1a067be8c

[errors] stop using deprecated ERR_HANDLE_CLOSED

Instead use ERR_CANCELED, its new name.

Change-Id: I2671a6eded761b6b06737c93b3289c2b8a46d8bd

[docs][syscalls] Fix all the manpages

Change-Id: Ie9ba25060f3331de8d9c178caf6332fb48fc80f5

[syscalls] rename mx_handle_wait_*() to mx_object_wait_*()

These act on the object the handle refers to, not the handle itself.

Compatibility wrappers are provided to ensure existing code
continues to compile, link, and run. Later we will deprecate
the wrappers and eventually remove them.

Change-Id: Icf69e75f7e0c060ba6026343f9d26ff9da4317d9