A few improvements to allow work with IE and FF in complex scenarios

1. Introduction of 'undefined' parameter to allow direct comparison
2. Nicety: a use of $.proxy() to eliminate use of the 'that' var
3. _Axis is supplied with the var keyword (to prevent global scope
pollution)
4. .convertColor() function rewritten to eliminate use of eval() AND
consider 'transparent' value of a color
5. If initial bg-color is 'transparent' alpha is set to 0, and color -
to #ffffff
6. Color calculation in init goes without eval now (there's no eval()
now in Flippy)