Periodic wraparound #47
Description
Periodic boundaries are currently implemented with a relation u[1] ~ u[end], and u[end] is on the interior. The boundary upwinding leads to instability on the upper index with the brusselator, so we need to move to wrapping around at the boundary so that the centered stencil is always used.
I'm doing this by creating a Val{Bool} ecapsulating whether a dimension is periodic in #45 and indexing through a function that dispatches on Val{true} and Val{false}, hopefully leading to the compiler removing this check.