Update odesolvers. Work arrya + fix tests + doc + pep8 things

docs/sphinx/figures/cluster_general.jpg

docs/sphinx/figures/cluster_general.pdf

docs/sphinx/figures/comm_split.graffle

docs/sphinx/figures/comm_split.jpg

docs/sphinx/figures/comm_split.pdf

docs/sphinx/figures/data_discr.graffle

docs/sphinx/figures/data_discr.jpg

docs/sphinx/figures/data_discr.pdf

docs/sphinx/figures/decomp_domain.jpg

docs/sphinx/figures/decomp_domain.pdf

docs/sphinx/figures/ghost_points.graffle

docs/sphinx/figures/ghost_points.jpg

docs/sphinx/figures/ghost_points.pdf

docs/sphinx/figures/periodic_topo.graffle

docs/sphinx/figures/periodic_topo.jpg

docs/sphinx/figures/periodic_topo.pdf

docs/sphinx/users_guide/domains.rst

docs/sphinx/users_guide/odesolvers.rst

docs/sphinx/users_guide/redistribute.rst

docs/sphinx/users_guide/subsets.rst