Remove #defines from assertion logic?

[drubinstein]

The assertion logic currently uses #defines heavily. Alternatively, we could've made template structs and stick the static_asserts in the structs. You can then use these as default template arguments (similar to enable_if) or as using declarations inside functions or classes.

Evaluate, discuss and implement or invalidate.

[calebzulawski]

For now, I've at least renamed them from ASSERT_(condition) to COTILA_DETAIL_ASSERT_(condition) to avoid any macro name reuse.