Add SIGUSR1 for update

List of plugins to implement:

     MPD
     Alarm clock
     portage
     iostat [-x] [-d] [-N] -zk [-p | <devices>...] <interval>
     SMART monitoring
     Battery
     /proc/acpi (mute)
     System tray
     Eyes
     Launchers
     Taskbar (as in rarity)
     Application menu
     UPS
     Blueshift integration
     Backlight control
     Thermal monitoring (`sensors`)
     ESSID
     Keyboard layout
     EWMH
     Meteor showers
     Lunar and solar eclipses
     e-mail
     Identify active and visible windows
     Calendars: holidays, birthdays, name days, events
     Summer time / standard time announcement (should support double
         summer time and similar)
     natural disaster reports
     IRC
     /proc/interrupts
     /proc/net/sockstat
     /proc/net/sockstat6
     /proc/net/wireless
     /proc/net/arp
     /proc/net/rarp (requires RARP to be configured into the kernel)
     /proc/net/igmp
     /proc/net/raw
     /proc/net/snmp
     /proc/net/tcp
     /proc/net/udp
     /proc/net/unix
     /proc/sysvipc
     /proc/locks
     /proc/swaps
     /proc/sys/kernel/random/

Demo plugins:

     linereader
     snmp6
     snmp
     softirqs
     solar
     vmstat
     weather
     hdparm
     alsa :: get_mute, set_mute, set_volume

Terminal mode