Make unit tests from all examples

[s-martin]

Examples 1, 4, 5, 7 (?) are already used also as unit tests.

Do this for all existing examples.

Restructure unit test files in a meaningful manner.

[s-martin]

Possible improvement:

Separate for each example the main method from the example, e.g. provide function objective and exampleXX, which should be placed in a .hpp file.

exampleXX should use seed and all command line options as input parameters and return ga.statistics() or something similar.

Therefore the implementation in exampleXX could be used both in the example executable (main in .C file) and in addition be used in a unit test with a static seed.

Currently the first examples used in unit tests duplicate the code, which is unfortunate. This should be reworked.

[s-martin]

Make unit tests from ex6 and ex8, so lists and trees are finally tested a bit.

Then merge this into the reworking list branch (#25) and finally continue on list refactoring, see #24