minor changes in iterators and pie.update()

- Itarator now sets the cursor for currentslice within the iterators
correctly when using next/previous
- update() now uses pies startingpercentage instead of first slices
Fixed visual glitch between parts of slices > 50%

- tried to fix vis. glitches between seperate slices without result
replaced alert()s with console.log()s
Added pie.setSize()

- pie.setSize() lets you change the size of the pie
- changed border-radius to percent for more flexible usage possibilities
Changed createPieObject()

- changed behaviour to use number of Slices as reference for percent and
colors. Method now creates slices by looping over the percentage and
color-array to reuse values if too few are given
minor changes