Add more unicode to us(dvp) layout.

Add more unicode to us(dvp) layout.

This commit adds the following definitions to the alternative group of
the us(dvp) layout:

  Shift+AC11  is en dash      mnemonic: <EC11> is -
  Shift+AD02  is ...          was: dead caron  mnemonic: <AD02> is ,
  Shift+AE11  is reverse interrobang  mnemonic: <AE11> is !
  Shift+AD11  is interrobang  mnemonic: Shift+<AD11> is ?

  Shift+AB07  is micro        mnemonic: <AB07> is m

Note about ellipsis which replace existing dead caron:

  The us(dvp) inherited some definitions from us(dvorak) simply because
  it omitted definition of all 4 levels for given key:

    key <AD02> { [ comma,           less,           guillemotleft               ] };

  which specifies only two levels so the third and fourth happens to be
  inherited from us(dvorak)'s definitions:

    key <AD02> { [	comma,	less,   dead_cedilla, dead_caron	] };

  I'm assuming that this was actually not intentional behaviour
  especially since the overwritten key is available in us(dvp) under
  another key (which make more sense):

    key <AD12> { [ at,              asciicircum,    dead_circumflex, dead_caron ] };

  Because of that, I've decided to go ahead and break that behaviour in
  favour of adding a new key.