Multiplexer VHDL example: SFE401

Using ghdl, these compile with commands:

ghdl -a multiplexer.vhdl
ghdl -e mux
ghdl -a mux_tb.vhdl
ghdl -e mux_tb

Run the commands with with:

ghdl -r mux_tb

ghdl quick start guide is available at https://ghdl-rad.readthedocs.io/en/stable/using/QuickStartGuide.html