Add tests

[jacogeld]

Both high-level (system) and low-level (unit) tests are missing.

[jacogeld]

This requires significant refactoring.

[jacogeld]

Travis CI has been set up and seems to be working correctly. Some simple unit tests have been added. Style checking has also been added to the system. More tests are required, most importantly system tests.

[jacogeld]

Previous system tests did not work, even though it appeared that they did. They are now more stable. We shall consider issue closed once all the testing code among the examples have been moved to the tests. Adding more tests will never truly be closed.

[jacogeld]

System tests are now working well. More tests need to be added but as per the previous comment, we should be able to complete this soon.

[jacogeld]

Postponed to the next release.