class TTRAP: public TBRIK

 TRAP is a general trapezoid. The faces perpendicular to z are trapezia and
 their centres are not necessarily on a line parallel to the z axis.
 This shape has 14 parameters.

     - name       name of the shape
     - title      shape's title
     - material  (see TMaterial)
     - dz         half-length along the z axis
     - theta      polar angle of the line joining the centre of the face
                  at -DZ to the centre of the one at +DZ
     - phi        azimuthal angle of the line joining the centre of the face
                  at -DZ to the centre of the one at +DZ
     - h1         half-length along y of the face at -DZ
     - bl1        half-length along x of the side at -H1 in y of the face
                  at -DZ in z
     - tl1        half-length along x of the side at +H1 in y of the face
                  at -DZ in z
     - alpha1     angle with respect to the y axis from the centre of the
                  side at -H1 in y to the centre of the side at +H1 in y
                  of the face at -DZ in z
     - h2         half-length along y of the face at +DZ
     - bl2        half-length along x of the side at -H2 in y of the
                  face at +DZ in z
     - tl2        half-length along x of the side at +H2 in y of the face
                  at +DZ in z
     - alpha2     angle with respect to the y axis from the centre of the side
                  at -H2 in y to the centre of the side at +H2 in y of the
                  face at +DZ in z