pull from the DC_Stepper_Motor program and set up as library

Dependencies:  

Revision:
0:80182fb5ee8f
diff -r 000000000000 -r 80182fb5ee8f QEI.lib
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/QEI.lib	Wed May 19 09:49:44 2021 +0000
@@ -0,0 +1,1 @@
+https://os.mbed.com/users/stivending/code/QEI/#bee7b70a365b