Incorrect docstring for `regulariser()` in oilmm.jl

[mjp98]

The docstring for regulariser(...) in oilmm.jl does not match the function signature used:

  """
      regulariser(fx, y)
  Computes the regularisation term of the logpdf.
  See e.g. appendix A.4 of [1] - Bruinsma et al 2020.
  """
  function regulariser(
      H::Orthogonal{T},
      σ²::T,
      Y::AbstractMatrix{T},
  ) where {T<:Real}

This function signature in the docstring matches that of regulariser(...) in ilmm.jl.

Perhaps it would be worth adding a new method for regulariser(fx::FiniteGP{<:OILMM}, y)?

[willtebbutt]

That sounds like an excellent idea. You can probably just remove this method, and replace it with your proposed method.

In fact, it might make sense to replace y with Y::AbstractMatrix{<:Real} (or something like that) in both cases.