Ufl

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- Rename ElementRestriction --> RestrictedElement
- Experimental import of x from tetrahedron
- Make lhs/rhs work for resrictions
- Redefine operator + for FiniteElements and replace + by *
- Rename ElementUnion -> EnrichedElement
- Add support for tan() and inverse trigonometric functions

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- Attach form data to preprocessed form, accessible by form.form_data()

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- Fix bug in propagate_restriction

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- Several interface changes in FormData class
- Introduce call preprocess(form) to be called at beginning of compilation
- Rename BasisFunction --> Argument
- Rename Function --> Coefficient

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- Redefine grad().T --> grad()
- New meaning of estimate_max_polynomial_degree
- New function estimate_total_polynomial_degree
- Allow degree = None and cell = None for elements

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- Extensions for ElementRestriction (restrict FiniteElement to Cell)
- Bug fix for lhs/rhs with list tensor types
- Add new log function set_prefix
- Add new log function log(level, message)
- Added macro cell integral ``*dE``
- Added mechanism to add additional integral types
- Added LiftingOperator and LiftingFunction
- Added ElementRestriction