[Utils] NumberMath

[vsubhuman]

DoubleMath goes well with doubles (obviously), but there should be some tool to work with common numbers (or any numbers) without using pretty dangerous for general cases DoubleMath#asDouble all the time.

Implement class NumberMath with these methods:

1. #equals(Number, Number):boolean
2. #greaterThan(Number, Number):boolean
3. #greaterThanOrEquals(Number, Number):boolean
4. #lessThan(Number, Number):boolean
5. #lessThanOrEquals(Number, Number):boolean
6. #isZero(Number):boolean
7. #isPositive(Number):boolean
8. #isNegative(Number):boolean

Rules for comparison are these:

1. Two nulls are equal.
2. Null is neither greater, nor lower than any other number or null.
3. Double.NaN is equal to itself, by double comparison rules.
4. Float.NaN is equal to itself, by float comparison rules.
5. Float.NaN is equal to Double.NaN, by float widening rules.
6. Both Double.NaN and Float.NaN are neither greater, nor lower than any other number or NaN.
7. If both numbers are of the same class that implements Comparable and it's not Double or Float - they should be compared by their implementation.
8. DoubleMath.compare should be used for any other cases.

Note: this class may be dangerous for it uses exceptional rules for native doubles and floats and generalizes any other numbers.

Note: this class may be dangerous for it will compare any numbers of different kind by their double value, which may be invalid. Though util is coined to cover 95% of generally simple cases where numbers are neither greater than max double, nor lower than min double, and generally may be intercompared.

Related to: #115

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Also implement class NumberMath.Instance that may be instantiated with predefined EPS.

Related to: #116