The library has been cleaned up as it has got a bit untidy due to the large number of small incremental changes.
4bit Sprite examples renaed to be consistent with others.
alphaBlend example moved to generic folder (alphaBlend fn was moved to TFT_eSPI class).
Added sections + explanatory comments to functions prototypes.
Temporary comments added for potential gotchas for noobs when using DMA.
spi_begin/end functions renamed to reflect functionality. Old fns retained for backwards compatibility with user setup.h files.
