Official freeRam() command

All mcu project may pay attention on Ram use, and have an official command for print freeRam at runtime it is very important.
For avr there is a well know freeram function, but it do not work on other architecture, like Zero, Due, etc.

So i think that an official freeRam() function is actually very needed inside the Arduino core, and this also would push third-party core authors to work on their implementation of freeRam().

El issue no especifica ningún archivo, prueba ni punto de entrada de la API. Empieza comparando el enfoque existente de AVR para freeRam con las cuestiones de arquitectura de Zero y Due descritas aquí; se considera terminado cuando exista una API freeRam() acordada para todo el core, con implementaciones compatibles con todas las arquitecturas afectadas.

Escrito por el modelo de indexación a partir del texto del issue.