Fix clipping issue for circleFill when top is offscreen.

Replaced circleFill algorithm with a scanning algorithm. Also fixes
problem with XOR draw mode for filled circles.
Added keywords for existing functions
Added missing setColumnAddress, setPageAddress and data keywords.
Moved getScreenBuffer keyword to a more appropriate location.
Removed duplicate "invert" keyword
Merge branch 'emilong-circle-fill'
added version history
Merge pull request #15 from MLXXXp/add_keywords

Add keywords for existing functions