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- Added nabla_grad and nabla_div operators
- Added error function erf(x)
- Added bessel functions of first and second kind, normal and modified,
bessel_J(nu, x), bessel_Y(nu, x), bessel_I(nu, x), bessel_K(nu, x)
- Extended derivative() to allow indexed coefficient(s) as differentiation variable
- Made ``*Constant`` use the ``Real`` space instead of ``DG0``
- Bugfix in adjoint where test and trial functions were in different spaces
- Bugfix in replace where the argument to a grad was replaced with 0
- Bugfix in reconstruction of tensor elements
- Some other minor bugfixes