Added tests that investigate multiple ranges

- Min endpoints may never be omitted.
- Max endpoints may be omitted, but generating a value can fail.
Mostly updated javadoc comments

- Added links to related tests.
- Also tweaked the rangesWithMissingMaxFailRandomly test.
    Increased the number of generated values to increase reliability.
Added tests investigating expressions in ranges

Expressions are not evaluated for a parameter with multiple range.
References to other parameters are therefore not allowed either.
Minor comment tweaks
Added multiple tests

- Demonstrate that array elements are defined the same way as
    regular parameters (supporting expressions and multiple ranges).
- Demonstrate that expressions consisting of a single parameter
    reference cannot be evaluated.
- DesignSpace.next() can return invalid values for a parameter
    that is defined using an expression.