Merge branch 'dev'
Add libc string code
UART buffer size can be set by Makefile
kiostream added when we select uart driver
Clean flash & iap code.
Add UART function
Add float output for printf
Check float / double
Rename math include file to fix libm linking problem
Fix memory protocol
Add timer 16 bits.
Add GPIO option
Fix gpio option bit clear
Add a default gpio mode
Add pwm32 gpio output
Add raw pwm duty cycle
Add define for event stack size
Merge branch 'master' into dev