Todo:
=====
 * Add hook for channel ACK
 * Finish auto-reinit in protocol engine
 * Finish ping framework
 * Check PSC commands
 * Use Serial object in multiplexer as well
 * Implement Cinterion Basic 07.10 extensions
 * Improve concurrent throughput fairness and reduce latency
 * Add org.freesmartphone.GSM.MUX.GetAllocation() -> a(s: origin, i: channel, s: ptypath)

Problems due to Vala:
=====================
 * No async dbus on server side
 * No proper dbus errors

Features of this Multiplexer:
=============================
 * Clean Architecture seperating
   - Protocol engine,
   - Serial port,
   - Virtual Channel,
   - Session handling, and
   - DBus Server.
 * Automatic modem power handling is optional and can be
   configured in /etc/abyss.conf.
 * Top priority is getting frames from the modem,
   so it doesn't need to wait for us.
 * No channel ACK race conditions, a pty will only be allocated
   once we get the first serial status package from the modem.
 * No pty overruns possible [as long as we have main memory left],
   channels will buffer everything in memory and deliver
   the chunks asynchronous.
 * Supports requesting individual channels in addition to
   the 'the next free one'. This is helpful since virtual
   channels keep state over opening/closing.
 * Ping framework (on modems that support it) for detecting
   stuck connections and transparent reinit.