
I would like you to implement a module named TopModule with the following
interface. All input and output ports are one bit unless otherwise
specified.

 - input  a   (100 bits)
 - input  b   (100 bits)
 - input  sel
 - output out (100 bits)

The module should implement a 2-1 multiplexer. When sel=0, choose a. When
sel=1, choose b.

