Changed from_elements signature
At this point there is no support for other elements sets so the new
signature greatly improves readability of the function, consistency
with from_vectors and simplifies behaviour. We can think of changing
it later.
Added missing lines to tox report
Added mean motion to `State` objects
Fixed examples to reflect 64dc66c
Improved bodies docstrings
Refactored PQW vectors computation
Added plot2D method to State
I don't feel totally comfortable with this method being there, but
for now it just works. Still untested though.
Added plot as a shortcut to plot2D