Provide a mechanism for the outside world to write program in instruction memory

[hadirkhan10]

Write now Picofoxy supports reading program files through the $readmemh construct. This is useful for simulations but gets tedious quickly when you change a program and have re-run the whole synthesis, place and route, and bitstream generation phases. For this purposes an ideal solution would be to support a flash interface on the arty board but this can get complicated too quickly. The other thing we can do is to create a UART programmer that takes the program from the user through USB-UART bridge and then initialize the contents of the memory with that program.