Lowered threshold for singularity detection.

The threshold for the detection of a singularity was lowered from 1e-12
to 1e-17. This was done in the hope to reduce the drift of the field
line trace on the separatrix.
Completed documentation, format needs to be fixed.
Finished documentation.

The doxygen documentation is now finished.
The format is working and the creation of the documentation runs without
errors or warnings.