- `BigRational::parse()` is now `of()`
- `BigRational::of()` is now `nd()`
This keeps BigRational in line with BigInteger and BigDecimal, whose `of()` factory method accepts a single parameter.
The new way to create a BigRational from two numbers is now called `nd()` for numerator/denominator.
Shorthand "int" and "bool" are now used instead of "integer" and "boolean".
This makes more sense as the latter are not accepted as synonyms in PHP 7 scalar type hints and return types.
