There are quite a few linked-lists of things that want events after
some period. This introduces a type binding an lws_dll2 for the
list and a lws_usec_t for the duration.
The wsi timeouts, the hrtimer and the sequencer timeouts are converted
to use these, also in the common event wait calculation.
lws_dll2 removes the downsides of lws_dll and adds new features like a
running member count and explicit owner type... it's cleaner and more
robust (eg, nodes know their owner, so they can casually switch between
list owners and remove themselves without the code knowing the owner).
This deprecates lws_dll, but since it's public it allows it to continue
to be built for 4.0 release if you give cmake LWS_WITH_DEPRECATED_LWS_DLL.
All remaining internal users of lws_dll are migrated to lws_dll2.
This adds support for the integrating libdbus into the lws event loop.
Unlike the other roles, lws doesn't completely adopt the fd and libdbus insists
to retain control over the fd lifecycle. However libdbus provides apis for
foreign code (lws) to provide event loop services to libdbus for the fd.
Accordingly, unlike the other roles rx and writeable are not subsumed into
lws callback messages and the events remain the property of libdbus.
A context struct wrapper is provided that is available in the libdbus
callbacks to bridge between the lws and dbus worlds, along with
a minimal example dbus client and server.
