#31 Warn about unwise API changes

[Matthew Doar]

There are some kinds of API changes that are riskier than others.
For example, chaning

void foo(String name, String gender)

in one release, to

void foo(String gender, String name)

in another is a bad idea. No warnings will be generated when the
changed API is used. Perhaps JDiff could warn of this.

The ParamAPI toString method is where the comparion is based.