Felupe

Added
- Add template regions, i.e. a region with a `Hexahedron()` element and a quadrature scheme `GaussLegendre(order=1, dim=3)` as `RegionHexahedron`, etc.
- Add biaxial and planar loadcases (like uniaxial).
- Add a minimal README-example (Hello FElupe!).

Changed
- Deactivate clamped boundary (`clamped=False`) as default option for uniaxial loading `dof.uniaxial`.

Added
- Add inverse quadrature method `quadrature.inv()` for Gauss-Legendre schemes.
- Add discontinous representation of a mesh as mesh method `mesh.as_discontinous()`.
- Add `tools.project()` to project (and average) values at quadrature points to mesh points.

Changed
- Removed `quadpy` dependency and use built-in polynomials of `numpy` for Gauss-Legendre calculation.

Fixed
- Fix typo in first shear component of `math.tovoigt()` function.
- Fix wrong stress projection in `tools.topoints()` due to different quadrature and cell ordering.

Fixed
- Fix import of dof-module if `sparse` is not installed.

Added
- Start using a Changelog.
- Added docstrings for essential classes, methods and functions.
- Add array with point locations for all elements.

Changed
- Rename element methods (from `basis` to `function` and from `basisprime` to `gradient`).
- Make constitutive materials more flexible (allow material parameters to be passed at stress and elasticity evaluation `umat.gradient(F, mu=1.0)`).
- Rename `ndim` to `dim`.
- Simplify element base classes.
- Speed-up calculation of indices (rows, cols) for Fields and Forms (about 10x faster now).
- Update `test_element.py` according to changes in element methods.

Removed
- Automatic check if the gradient of a region can be calculated based on the dimensions. The `grad` argument in `region(grad=False)` has to be enforced by the user.