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

ZX-2399 #comment

Test: no functional change
Change-Id: I1f285c677e2444fcf1d720d7ecbd9f490c303962

[syscalls] Update parameter types and names

This CL updates the parameter types and names for a number of syscalls
to match the Zircon System API rubric. There's more work to do to make
all the syscalls conform to the rubric, but this change is a start.

Change-Id: I218ac5e7e0cbd80a8c69fef7891ad40b78b6b407

[futex] Mark futex paramaters as IN only

Change-Id: I37a626cbd467eeccb4872b39d02d2b5e50289e45

[docs] small assorted fixes

Change-Id: I90c370aa4eb52d4f276769aa82c3b2ab07369052
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>

[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

[docs][syscalls] Fix all the manpages

Change-Id: Ie9ba25060f3331de8d9c178caf6332fb48fc80f5

[kernel][futex] Enforce alignment of pointers passed to futex.

Ensure that the user_ptrs passed to FutexWait, FutexWake, and FutexRequeue are
aligned.

MG-452 #comment

Change-Id: Ic3ebe0e769e89fc9f0feaddac2968a0997d77044

[docs][syscalls] Update futex syscall docs

This makes two changes. First, it changes the declarations of these to
use the mx_futex_t type (this type exists since we currently can't name
an atomic integer the same way between userspace C code and kernelspace
C++ code).

Second, it changes the documentation of the possible return values of
wait and wake. These were changed en masse with many other functions,
but in this case the change is inappropriate. More importantly, it also
does not match what the functions actually return. Returning
ERR_ALREADY_BOUND ("the named entity is already owned or controlled by
another entity") implies that futexes necessarily exist in an owned
state that is correlated to the value located at that address. But they
don't actually have such an ownership semantics, and the kernel only
needs to be able to tell you if you are racing during the call. As such
ERR_BAD_STATE ("the system is unable to perform the operation in its
current state"), which the functions in fact already return, makes more
sense.

Change-Id: I2d5aba79217499bb9c64469d01fbfd101fd02811

sync errors.md with fuchsia-types.def

ERR_NOT_ENOUGH_BUFFER -> ERR_BUFFER_TOO_SMALL
ERR_FLOW_CONTROL -> ERR_SHOULD_WAIT
ERR_NOT_READY -> ERR_UNAVAILABLE
ERR_NOT_AVAILABLE -> ERR_ALREADY_BOUND
ERR_I2C_NACK -> ERR_IO_REFUSED
ERR_CHECKSUM_FAIL -> ERR_IO_DATA_INTEGRITY

Add ERR_IO_DATA_LOSS
Remove ERR_CANCELLED

Change-Id: Ibe27bc5198cc4d83ed384bf2858cfca0a8694d4c

remove "garbage bin" error codes

Change-Id: Ic0866221523031612a7fd1097be654229911fc0d

[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

[docs] move magenta docs up a level, make them more front and center

(and make the paths shorter for doc urls, editing, etc)

Change-Id: I1416d8e93aa8732e2735027e6356d629adebea41