v1.1.1

Personalization Fixes:

• _build_sg_personalization "to" arg now changed to optional; either it or existing_personalizations must be set.
• Prevent using .personalizations without tos set.
• Prevent unnecessary resetting of tos when personalization is already constructed.
• No longer provide tos if not set for personalizations. This is to prevent every personalization from being sent to every recipient in msg.to
• Added/Changed some comments/docstrings to reduce ambiguity

Thanks @alichass for the contribution!