pulse consistency test using wait_us

Revision:
0:18409537564c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SoftPWM.lib	Sat Mar 30 06:37:35 2019 +0000
@@ -0,0 +1,1 @@
+https://os.mbed.com/users/komaida424/code/SoftPWM/#7918ce37626c