v0.10.9: Remove obsolete classes ScalarField and VectorField (#92)

Fix #50

v0.10.8: Some bug-fixes for Psydac (#91)

In order to avoid problems when assembling vector expressions over the boundary, we do not create `Trace` objects from the expressions. Such a kind of reverse engineering is complex and error prone, and not really needed at the moment.

* Fix bug in Integral.subs_boundary_expr
* Set Trace commutativity from its expression
* Let IndexedTestTrial use indices of type sympy.Integer
* Don't substitute u with Trace(u) in boundary integral
* Deactivate unit tests for Trace
* Update version.py

v0.10.7: Add __neg__ method to Integral (#89)

* Allow taking the negative value of an Integral object: the minus sign is applied to the integrand expression;
* Update version.

v0.10.6: Feec dirichlet (#88)

- Delete mapping when computing logical expr of forms;
- Update version.

v0.10.5: Feec dirichlet (#87)

The following changes were made:
  - Delete node annotation;
  - Compute boundary jacobian when dim = 1;
  - Update library version.

v0.10.4: Fix bugs in Hcurl & Hdiv pullbacks (#86)

These bugs were introduced in the previous PR, in an unfortunate attempt to make the code more readable...

v0.10.3: Fix bug in L2 pullback (#85)

* Fix bug in L2 pullback: divide function by determinant instead of multiplying it
* Some cleanup in PullBack constructor
* Update version.py

v0.10.2: Update version.py (#84)

Change version to 0.10.2, require sympy version < 1.17.

v0.10.1: Multi-patch mapping (#80)

- Add MultiPatchMapping class to handle mappings in the multi-patch case
- Fix bug in Grad and LogicalGrad for the VectorTestFunction case
- Support sympy-1.6
- Update version.py

v0.10.0: Add logical operators (#71)

Implementation of logical operators:
- Add 1d, 2d, 3d logical operators
- Add Piola transformations
- Allow application of `LogicalExpr` on vectorized operators like `grad, div, curl, dot,  ...`
- Add `MatrixSymbolicExpr` class and Symbolic jacobian Matrix
- Update `TerminalExpr` to handle physical and logical coordinates
- Add mappig attribute to Domain class which is set to None if it's a logical domain
- `Domain.coordinates` can have two sets of coordinates `x1, x2, x3` if it's a logical domain
 or `x, y, z` if it's a physical domain 

Moreover:
- Sort `Union` args by their string representation (fixes recurring failure in unit test)
- Update .travis.yml (don't use "sudo", also test on Python-3.8; always use Linux Xenial 16.04)
- Update version.py

Co-authored-by: Yaman Güçlü <[email protected]>