Faster text rendering through text-block buffers.

[8bitmcu]

Hi there,

The write() method currently writes to the screen character by character. In some past experiments, I've found that there is a lot of delays between spi transactions. As such I began experimenting with using larger text buffers: this commit is a proof of concept where I am buffering a whole line of text at a time before committing any spi transactions.

I am certainly not suggesting to take my changes as is: This requires an especially large buffer, and I'm sure that there are situations which is probably a drawback of using this technique (such as using large font with few characters). But I would like the authors to consider this technique as I've found that performance can be improved up to ~2x in some situations, especially when using smaller fonts / lots of characters