[Core:struct] Message Structure

[john-bv]

• [x] Ability to post a message
• [x] Ability to edit the message object
• [x] Ability to pin the message
• [x] Ability to reply to the message with a given reference message and guild id
• [x] Ability to delete the message with a return value of true or false
• [x] Ability to get the message author from the message
• [x] Ability to get a circular guild reference on the message object. (redacted)

REF: https://github.com/Bavfalcon9/Assistant/issues/19