code cleanup
fix docstring typo
bug fix: prevent propagator from reusing RHS functions unless rhs_reuse is explicitly set to True in the given Odeoptions
tentative: warn user that RHS is reused if Odeoptions.rhs_reuse=True, since this can give unexpected behaviour. This warning might be dropped in favor for a warning in the docstring.
small API change: rename keyword argument opt to options to be consistent with other solvers