Disconnect boundary condition handling from L operator

[ChrisRackauckas]

No description provided.

[ChrisRackauckas]

This is getting the wrong boundary coefficients. MWE:

using DiffEqOperators
stencil_length = 3
dummy_x = -div(stencil_length,2) : div(stencil_length,2)
deriv_spots = -div(stencil_length,2) : -1
DiffEqOperators.calculate_weights(2, 0.0, dummy_x)
[DiffEqOperators.calculate_weights(2, 1.0x0, dummy_x) for x0 in deriv_spots]

should be the left centered stencil for the last one?

[ChrisRackauckas]

Centering by changing the x seems off as well:

using DiffEqOperators
stencil_length = 3
dummy_x = -div(stencil_length,2) : div(stencil_length,2)
deriv_spots = [dummy_x .+ i for i in 1:div(stencil_length,2)]
DiffEqOperators.calculate_weights(2, 0.0, dummy_x)
[DiffEqOperators.calculate_weights(2, 0.0, x) for x in deriv_spots]