- Overloaded Fraction class constructors to accept larger-ranged
integers.

- Added Fraction methods for obtaining the Fraction's value when and
only when it's a whole number: intValue(), longValue().

- Added Fraction methods for obtaining the Fraction's value, as a
floating-point ratio: floatValue(...), doubleValue(...).

Also added appropriate unit tests.
Fixes #54.  Note that Fraction.pow(...) relies on Math.pow(double, double),
because there doesn't seem to be a standard implementation of
BigDecimal.pow(...).
Fixed a minor big in the numberic range-checking in some Fraction methods.  Also added a test case to confirm tha Fraction.pow(...) throws an exception when its result is too big to fit in a double.
Resolve merge conflicts from merging 'master' into 'issue54'.
Trivial cleanup of commented-out code.
Merge pull request #62 from stepthom/issue54

Issue54