Rename setExpectedAPSRflags() to setExpectedXPSRflags()

The function can now be used to test the thumb mode EPSR bit in
addition to the APSR bits.
Add BLX support
Initial implementation of memory interface

Created the IMemory interface that can be used by pinkySim to read and
write from memory.  I also created the SimpleMemory object which
implements IMemory for the purpose of testing.
Use IMemory interface for fetching instructions