* [WIP] Draft for matmul

* Numpy-style broadcasting for matrix multiplication.

* 3D matrix multiplication with one big Dot/slice/concat.

* Generic ND matmul implementation using slice/dot/concat pattern.

* Code formatting.

* remove unused header

* Add missing header

* Utility reshape-like functions.

* Use utility functions.

* Review comments.

* Code format

* Use if/else instead of ternary operator for readability.

* Remove unused function overloading

* Utility function expanding tensor shape with empty axes.

* Use helper functions.

* Use type for auto variable initializer to fix Centos build

* Fix Centos build errors.