Shenfun

Working on Coordinates - allowing sympy measures to be defined for simplify
Add some plotting tools making use of plotly

Changing names

MixedTensorProductSpace -> CompositeSpace
VectorTensorProductSpace -> VectorSpace

and introducing a space for second order tensors

TensorSpace

For now it is only possible to project to this second order space. Solving PDEs for second order tensors would require shaping up operators (grad, div, curl).

This release gets rid of an ugly bug in setup.py, which caused conda-forge builds to use the compiler option `-march=native`. Without this option there should be much less segfaults around, as seen in issue 26 (https://github.com/spectralDNS/shenfun/issues/26)