allow multitouch in pressing buttons as alternative to moving touch
add Gamma/Factorial functions extension to Master Library
Implement HIR support.

The HIR instruction are officially undocumented but are well known and
described and used in many programs. The HIR instructions are just dealing
with the 8 stack internal registers.

The operations are:

   HIR CN : 82 CN

Where N is in range 0 .. 7 and correspond to the 8 internal registers with
0 being the currently displayed value (X).

And C is:
  0  : STO : X         -> Stack (N)
  1  : RCL : Stack (N) -> X
  3  : ADD : Stack (N) += X
  4  : MUL : Stack (N) *= X
  5  : SUB : Stack (N) -= X
  6  : DIV : Stack (N) /= X