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)
Changes in line #678: if we assume the opts.verso is jQuery object it makes sense to pass it as-is.
See, the call to .html() method only narrows the types of content which can be passed on to the plugin to.. text.
In fact, gotten rid of .html(), we now can pass anything the jQuery .append() method can handle (primarily another jQuery object and not a simple HTML markup). A possibly deep-cloned DOM object WITH events hooked to it? Hmm. It allows us to interact with the verso side.
Merge pull request #7 from AndrewRevinsky/master

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