Merge branch 'feature/convergence_test' into 'develop'

CMakeLists.txt

TurTLE/DNS.py

TurTLE/PP.py

TurTLE/test/particle_set/NSVEparticle_set.cpp

TurTLE/tools.py

cpp/field.cpp

cpp/full_code/NSE.cpp

cpp/full_code/NSVEparticles.cpp

cpp/kspace.cpp

documentation/index.rst

documentation/sphinx_static/bibliography.rst

documentation/sphinx_static/convergence.rst

documentation/sphinx_static/convergence_fields.rst

documentation/sphinx_static/convergence_particles.rst

documentation/sphinx_static/err_vs_dt_field.svg

documentation/sphinx_static/err_vs_dt_particle.svg

documentation/sphinx_static/trajectories.svg

examples/convergence/fields_base.py

examples/convergence/fields_temporal.py

examples/convergence/particles_temporal.py