watcher: ignore repeated registration

Apparently the Blueman applet likes to register the same item about 20
times every time bluetooth gets toggled. This leads to rapid increase in
D-Bus watchers both for the watcher as well as DbusMenuGtk, and what
seems to be a memory race condition as a bonus. The spec is ambiguous
here, but for now we assume reregistering an item while it is still
alive can be ignored. Warning added in case this turns out to break
stuff in the wild.
set WM_CLASS hint to StatusNotifierItem.Id

This should fix some issues with creative traybar implementations.
See todo.sr.ht/~steef/snixembed/4.

Add Matrix room, try to be more clear on the --fork functionality, move
up the issue tracker and remove WIP from title to not scare off new
users too much (as it Just Works™ with many setups now).
icon theme tweaks

Get the theme from the icon's screen, and make it rescan if needed.
Pretty sure it doesn't know whether it's needed since Skype icons only
start showing up after ar restart.. but it works fine for others.
quick minimal appindicator patch

Currently supported: icon names and icon theme names, menus. Tooltips do
not appear to work, more research is needed in this department.

This patch also breaks the SNI item_registered D-Bus signal, meaning
less spec coverage. Then again, this signal does not seem to be used by
anything in the wild, and it could easily be made available if needed.
Until then, it's probably just some saved cycles.
add another workaround
workaround for libappindicator
icon name: check for null (Gtk warning)
freedesktop icons support
tooltip text support

All tested applications only seem to set tooltip titles instead of
tooltip text, but the tex is also included. Tooltip icons are not
supported, markup is supported except for <a> (just pumps the text
through Pango Markup parser, which doesn't support <a>). Can't click it
do not cache D-Bus properties

Apparently GDBusObjectProxy loads properties from a cache by default,
only updating values when some D-Bus changed signal arrives. Which never
will in a common case (QSystemTrayIcon).
README: add git as build dependency
SNI.Menu dbusmenu support through libdbusmenu-gtk3
fighting sr.ht markdown parser
fighting sr.ht markdown parser
fork: search in path
updated readme, makefile
README: markdown and more info
version from git describe
README: electron environment hack