library incompatible with ESP8266 (fixes included)

[gschintgen]

Hi,
I'm not sure if this library is still maintained. Still, I'd like to let you know that in its current state it's incompatible with ESP8266 based boards. The compiler complains about a missing <avr/pgmspace.h>
header file. In fact, for non-avr boards like the ESP8266, the correct header is simply <pgmspace.h>.
You could add support for those boards by replacing the #include directive by the following code:

#if (defined(__AVR__))
#include <avr\pgmspace.h>
#else
#include <pgmspace.h>
#endif

A second issue that came up is that the SPI frequency was set too high (100 MHz instead of the maximum 10 Mhz that the MAX7219 accepts according to its datasheet). Simply dropping a zero in line 207 fixes it:

SPI.beginTransaction(SPISettings(10000000, MSBFIRST, SPI_MODE0));

For the record, I'm using a Wemos D1 Mini to drive a common 4-in-1 module of 4 daisy-chained 8x8 red led matrices.

Anyway thanks for your library and have a nice holiday season.

[Stardisk]

THANK YOU @gschintgen
Your fixes work for WEMOS D1 R2!