add tests

[bmachiel]

I have already written some test data for:

• de-embedders
• touchstone and citi reading

These need to be cleaned up and pushed to the repository. In additon, extra tests need to be added for the remaining classes.

[bmachiel]

Basic tests for deembedding have been committed (56fd693). The test structures don't include reactive components, however. Also, the test verification needs to be improved. The S-parameter graphs of the deembedded data are very close to those of the DUT, but numerically they seem not to matched that well.

[bmachiel]

2efc9a619e9317cabbda adds deembedding tests on a realistic fixture.