[README] Renamed all readme files to indicate markup format.

examples/stm32/l1/stm32l-discovery/button-irq-printf-lowpower/README.md

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+This is _functionally_ identical to the "button-irq-printf"
+example, but has been modified to use some low power features.
+
+There is a 115200@8n1 console on PA2, which prints a tick count every second,
+and when the user push button is pressed, the time it is held down for is
+timed (in milliseconds)
+
+Instead of free running timers and busy loops, this version uses the RTC
+module and attempts to sleep as much as possible, including while the button
+is pressed.
+
+Status
+~~~~~~
+Only very basic power savings are done!
+
+Current consumption, led off/on, 16Mhz HSI:    2.7mA/5.4mA
+Current consumption, led off/on,  4Mhz HSI:    1.4mA/?.?mA
+Current consumption, led off/on,  4Mhz MSI:    0.9mA/?.?mA