feature: allow std::function for STM32

[shroomist]

naive poking showed that std::function works for stm32

[arkhipenko]

I don't use this, but thanks! Will review and merge.

[GitMoDu]

Please review Platform identifiers before merging, as discussed here.

[arkhipenko]

Please review Platform identifiers before merging, as discussed here.

Why would support for general architecture (if it is indeed supported) be worse than listing endless defines for each variety?

[GitMoDu]

It's an option that's more useful for libraries that depend more on Arduino core functionality, or not at all.
Since TaskScheduller basically only uses the millis()/micros() from the Arduino API, everything else being plain C++, I'd say I agree with you.
Just wanted to make sure you are aware how touchy the subject actually is, because it's a mess right now on STM32 side with 3, concurrent and incompatible Cores (STM32, Roger's and Steve's)

[arkhipenko]

ok.
yield() is empty in stm32 implementation, so I did not include the second update.
merged into 'testing' branch.