Added possibility to write an arbitrary screen buffer to display 

i created a new method "displayScreen" which takes an screen buffer "uint8_t* buffer" and writes it to the display. the existing "display" method now uses this new method with the internal screen buffer "screenmemory" as argument.

this enables one to create and manipulate their own screen buffers outside the MicroView library, wich presents whole new possibilities to create art, manipulate on bit level, and so on.

my editor killed millions of trailing spaces (like it should be), which makes the diff harder to read, sorry.