Add SIGUSR1 for update

List of plugins to implement:

     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 and link quality for wireless interfaces
     News feed syndication
     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/dri
     /proc/interrupts
     /proc/net/sockstat
     /proc/net/sockstat6
     /proc/net/wireless
     /proc/sysvipc

Demo plugins:

     linereader
     snmp6
     snmp
     softirqs
     solar
     vmstat
     weather
     hdparm

Terminal mode