Rename view_msg to view_email for consistency

[ncoop57]

Renames view_msg() and view_msgs() to view_email() and view_emails() for
better API consistency and clarity.

• Updates function names in core.py
• Updates documentation in README.md
• Updates tool list in init.py

This improves the API naming convention to use the more standard 'email' terminology throughout.

[jph00]

I actually think this needs to be changed everywhere. msgs->emails, Message->Email, etc. Consistency seems helpful. WDYT?