Fastor V0.6.4

Fastor V0.6.4 is an incremental change over V0.6.3. This release includes bug fixes and some new features

1. Sleef backend for SIMD implementation of trigonometric and hyperbolic functions
2. New tensor functions: squeeze, reshape and flatten [d8acd9f]. Refer to Wiki page for the documentation
3. More general support for complex-valued arithmetic and complex-valued tensor algebra such lu, solve etc [c03811b]
4. Add top level CMake file for distribution of Fastor [8bc161e]. Contributed by @mablanchard
5. Fix compile issue with type name printing [13b2a1c]. Contributed by @matthiasneuner
6. Fix bug in determinant [e96e63f]. Contributed by @wermos
7. Implement Singular-Value-Decomposition svd and Signed Singular-Value-Decomposition ssvd for small square matrices [6de6662]
8. Fix multiple bugs with TensorMaps [5980b41]