Add TestEspApi example, exercising the non-RTOS C API.

[nuket]

Wrote a little code to exercise the C API, using the CallSDKFunctions example as a starting point. It doesn't exercise every last function, but is helpful for learning how the C API works.

[ibaranov-cp]

This looks really good to me!

[nuket]

Thanks!

Curiosity: Is the latest 1.5.1 non-RTOS SDK planned to be merged into the codebase? I noticed some new forced-sleep API calls that might be interesting to use. Wondering if I could help out in porting this stuff.

It also seems like the PlatformIO guys are still using the esp8266/Arduino with the 1.3.0 version of the SDK? (off-topic, I know).

[igrr]

• We are actually using 1.5.1 at this time (see https://github.com/esp8266/Arduino/blob/master/tools/sdk/version)
• PlatformIO has been updated to use the latest 2.1.0 release yesterday (https://twitter.com/PlatformIO_Org/status/704304862998224896)

[krzychb]

@nuket

This part of code is my favourite 😄

Serial.begin(74880); 
system_update_cpu_freq(SYS_CPU_160MHZ); 

Nice example 👍

Krzysztof