New Ratio model class

New Ratio model class for representing ratios with more pride and elegance than just a floating point value.

• Has three value-type properties: antecedent(Value), consequent(Value), and quotient(Value).
	» The antecedent is the left (A) side of the ratio, consequent is the right (B) side; quotient is the two divided.  As such, there is interdependency between these; changing one always requires one other is re-calculated.
	» More simply: A:C == (A / C = Q)
	• Each stored as a double, and accessible as a double or NSNumber.
• Can be initialized via `initWith(Double|NSNumber)Antecedent:andConsequent:` in which the quotient is initially calculated, or by `initWith(Double|NSNumber)Quotient:` where the antecedent starts at `1.0` and the consequent is the inverse of the quotient (1 / Q). ???
• Internal setters for each property:
	• Check that the double floats are non-infinite/NaN/zero/sub-normal (we're really only interested in useful ratios) and flag as bad if not.
	• Antecedent and consequent changes recalculate the quotient (via ).
	• Quotient updates recalculate the consequent (via ).
• Triple unset and badSet state variables (one for each property) ensure that no mistake goes unnoticed; unset and invalid state queries or-check each.
• `goldenRatio` prefab creation method; currently returns a surrogate to a singleton.
	» I'm undecided as to whether this should return a newly-inited goldenRatio (which the new owner is free to modify at-will), or a non-modifiable surrogate to a singleton (since we can't have the golden ratio changing on us).