Modifications that produce ses3d input files with the correct event tag. (event_$ named correctly, correct event name in the event_list).

Correction of syntax errors in write_SPECFEM3D_CARTESIAN.py.
event_tag now an optional parameter + PEP8
Reformatting.
More PEP8.
Refactoring the SPECFEM writer.
Relaxation times as input parameters.
Merge branch 'master' of https://github.com/krischer/wfs_input_generator
Fixing critical bug in flake8 tester.

Now it actually works.
Lots of PEP8 fixes.
Q model variables reverted.

Fixing some other small issues.
Adding flake8 check to default test suite.
Slight reformatting.
Merge remote branch 'upstream/master'