Auxiliary functions for extents and strides were using different
functions. Additionally, many tags were used to distinguish between
different tensor types. This patch simplifies interfaces of different
core functions and unifies functions that can process different types of
extent and stride types.
* GSoC Phase 1: Enhance CI workflows and switch to Github Actions
More details of the work of this phase could be checked at my wiki https://github.com/BoostGSoC20/ublas/wiki
* Tensor tests use Github Actions
Old uBLAS will only use Travis and Appveyor from old legacy CI while
Tensor is now build using modern Github Action on wide array of compiler
and standards and codes.
* Add Copyright notice and refactor windows matrix
