Reorder and split Core libraries in the Reference

[novusnota]

For example, most of the things from core-advanced should be split elsewhere.
The core-common should be split into contextual, addressing and communication parts.

[novusnota]

Related to:

• Put emit into book/communication for better visibility #1141 — emit is already in the list of message-sending functions, which is referenced from a bunch of places. If there'll be a Core: Communication page in the Reference, that issue with visibility should be resolved IMO
• Move cryptographic functions from core-math into its own page #1692