[EXAMPLE:F0] Add basic example include
[EXAMPLE:F0] Add simple miniblink example
[EXAMPLE:F0] Add simple button example
[EXAMPLE:F0] Add simple usart example
[EXAMPLE:F0] Add usart printf example using newlib-nano
[EXAMPLE:F0] Add simple ADC example
[EXAMPLE:F0] Add example of using systick and MCO output on pin PA9.

This example is a merge of Chuck McManis's example for F4 and onnokort's system clock setting test blink example for demonstration issue, corrected in #224.

The LED in any available clock setting flashes four times per second.