screen refresh speed improvement

[jbeale1]

This may not be important, but if you want the display to refresh faster, you can remove all the separate screen updates which are now done at the end of every single character in this library, and do it only once after drawing the full set up words or numbers you are updating. I found this to look a lot better in my application.

[kwankiu]

I have fixed this in my implementation based on this library. You may want to check it out :

https://github.com/kwankiu/ssd1306wrap

PS: I can also submit a PR of my implementation and features added if @nickpmulder is interested in updating and maintaining this library.