add-Num#bigDecimalValue

[nimo23]

Fixes #.

Changes proposed in this pull request:

• added Num.bigDecimalValue() to convert the Num to a BigDecimal

  • For DecimalNum it returns its delegate
  • For DoubleNum it converts by BigDecimal.valueOf(delegate) (if delegate is NaN or Infinity, then it simply returns null)
  • For NaN it simply returns null.

• added an entry with related ticket number(s) to the unreleased section of CHANGES.md

Actually, it's not easy to get the BigDecimal-representation of a Num. We have intValue(), longValue(), doubleValue(), etc. so it also makes sense to add bigDecimalValue().

[nimo23]

Would it be better to overwrite bigDecimalValue() in its subclasses instead of providing a default method?

For example, in DecimalNum:

 @Override
 public BigDecimal bigDecimalValue() {
        return delegate;
}

With this, no if and cast is needed..

[TheCookieLab]

Would it be better to overwrite bigDecimalValue() in its subclasses instead of providing a default method?

For example, in DecimalNum:

 @Override
 public BigDecimal bigDecimalValue() {
        return delegate;
}

With this, no if and cast is needed..

Yes, that would be ideal.