DOCS: update changes.rst

Better to tell users straight away that mpv should not be treated
as just another MPlayer.
options: rename input-related options

--ar              → --input-appleremote
--consolecontrols → --input-terminal
--media-keys      → --input-media-keys
--joystick        → --input-joystick
--lirc            → --input-lirc
--lircconf        → --input-lirc-conf
--mouse-movements → --input-cursor
--right-alt-gr    → --input-right-alt-gr
options: rename subtitle-related options

--ass           → --sub-ass
--autosub       → --sub-auto
--autosub-match → --sub-auto-match
--sub           → --sub-file
--subcp         → --sub-codepage
--subfps        → --sub-fps
options: rename audio-related options/properties

Renamed options:
--audiofile       → --audio-file
--audiofile-cache → --audio-file-cache
--channels        → --audio-channels
--format          → --audio-format
--srate           → --audio-samplerate

Renamed properties:
samplerate → audio-samplerate
channels   → audio-channels
options: rename video-related options/properties

Renamed options:
--aspect    → --video-aspect
--fstype    → --x11-fstype
--native-fs → --fs-missioncontrol
--name      → --x11-name

Renamed properties:
aspect → video-aspect
options: rename msg-related options

--msgcolor    → --msg-color
--msglevel    → --msg-level
--msgmodule   → --msg-module
--msgtime     → --msg-time (also document this one)
--playing-msg → --term-playing-msg
--status-msg  → --term-status-msg
options: rename device-specific options

--dvdangle → --dvd-angle
--tvscan   → --tv-scan
options: remove obsolete --fsmode-dontuse
options: remove deprecated --identify

Also remove MSGL_SMODE and friends.

Note: The indent in options.rst was added to work around a bug in
ReportLab that causes the PDF manual build to fail.