x86 Slides: add diagram for x86 examples

[aaronbloomfield]

From aaronbloomfield#121:

• have a diagram that shows how C-style strings work for the compare_string() function
• have a diagram that shows what the stack looks like for the fib() function
• add a diagram about the little-Endian addressing benefits

A follow-up:

This did not get completed in time for the spring 2016 semester. We are moving to 64-bit assembly for the fall. So changing the target date for this to the fall 2016 semester, although it may not be relevant due to the assembly flavor switch