added ESP8266 support

[beyondszine]

Hi,
please let me know if there is something that I am missing with this PR

[beyondszine]

@omersiar
I checked it up in the ESP8266 arduino doc, this one is fixed and defined in sdk's spi_flash.h file.
I checked with other users also,
esp8266/Arduino#2421

[omersiar]

I believe SPI_FLASH_SEC_SIZE is fixed at 4096 bytes which is quite large comparing to Uno's EEPROM. Thank you for the improvement.

[beyondszine]

@omersiar while working and testing the codes, I have got some serious changes and trying to port a few of the examples as in this repository to esp8266. So how to go about these ?
I mean just update the older examples and the wiring diagram with pcb schematic ?

[omersiar]

These changes is not compatible with the current state of the Library, also cannot be merged to the master branch. On the other hand others can work on your branch, we need a proposal how to handle esp specific examples.

[beyondszine]

Thanks @omersiar I will take care of your suggestion and will try to implement it if I can.
Yeah, I understand now how my PR to master branch is not apt. I am developing it in my seperate branch and maybe we can incorporate that after full development.
What say ?

[TheNitek]

Not sure you know this, but you can wrap the ESP specific code like this:

#if defined(ESP8266)
	yield();
#endif

to prevent any influence on the other platforms

[beyondszine]

@TheNitek
I have indeed seen that in lines of code for ESP, but not yet sure about the yield function, cudn't get the chance to peek into it.
But thanks to you, I am surely going to keep this in mind for further codes.