Adding some contributors. Thanks to you all!
Wide character support.

Thanks "Eon S. Jeon" <esjeon@hyunmu.am>!
Add audible bell

\a is the character for bell, and st is only marking the window as urgent
if it is not active. This patch adds an audible bell which can be disable
with bellvolume variable.

Signed-off-by: Christoph Lohmann <20h@r-36.net>
Default volume of the bell is 0.
Fix some bugs in mouse tracking logic

* Button number in X10 mode:

  I believe the button - 1 came from "C b is button - 1" from [0].
  However, above this section, it states

    "Normally, parameters (such as pointer poisition and button number)
     for all mouse tracking escape sequences generated by xterm encode
     numeric parameters in a single character as value+32. For example, !
     specifies the value 1."

  Also, from the description of SGR,

    "The encoded button value in this case does not add 32 since that
     was useful only in the X10 scheme for ensuring that the byte
     containing the button value is a printable code."

  This suggests that we should still add 32 to the button value when in
  MODE_MOUSEX10.

* No button release reporting in X10 mode:

    "X10 compatibility mode sends an escape sequence only on button press,
     encoding the location and the mouse button pressed."

* Fix MODE_MOUSEMOTION:

  Currently, motion reporting is skipped when oldbutton == 3
  (corresponding to no button being pressed). However, oldbutton is
  only set on a button press, which will never be 3.

[0]: http://invisible-island.net/xterm/ctlseqs/ctlseqs.html