Define core module

[lgarithm]

The core module should be

• self contained
• feature complete
• minimal

syntax sugars and helpers should not be in the core module.

[lgarithm]

Now the header files has been split into 3 files (but still not clean enough)

• crystalnet.h (core APIs)
• crystalnet-internal.h (internal or test only APIs)
• crystalnet-ext.h (advanced APIs, e.g. layer)

There might be another header file

• crystalnet-dev.h (for advanced users to define extensions)

Beginner users will find crystalnet-ext.h much easier than crystalnet.h.

[lgarithm]

core types

shape_t
tensor_t
tensor_ref_t
operator_t