Update README.md

fixed some typos in README
Update README.md

backends is a more accurate name for the architecure section
fixed typo in makefile
call tests with python2

gdb extensions are only python2 so im going to defer porting this
thing to python3 until a time when its actually needed/useful
we dont know how many steps will happen in libc write call

all we can reliably test is that some amount of steps happen in
between the start of write and the end of write.
Merge branch 'master' into function_mockups