Fix for 27eea4f, guild fields

[ghost]

• Fixed missing ? for optional Guild#approximate_member_count
• Documented a new field that Mason put in an example somewhere:
  Guild#max_video_channel_users. I assume this is optional, but I
  am not sure of the exact situations; I assume it will not be null
  though.
• changed Guild#permissions to say "excludes overwrites" instead of
  mentioning channels specifically. Partially did this because I just spent
  10 minutes reformatting the table and didn't want to do it again;
  partially did this because it would not be sensible for it to take into
  account per-channel user-specific overwrites.
• updated wording to refer to guilds as guilds consistently
• updated to indicate "PUBLIC" guilds refers to the "PUBLIC" feature.
• changed approximate_presence_count to refer to members as non-offline
  as this also includes members in DND and idle, and it prevents
  being ambiguous or implying some relation to the status terminology
  and enumerations.
• documented that widget fields are null if not present
• documented that the guild embed is also known as the widget
• other consistency stuff

Hoping this will make stuff a bit more consistent as well to prevent the number of questions that new developers have :)

[advaith1]

Documented a new field that Mason put in an example somewhere:
Guild#max_video_channel_users. I assume this is optional, but I
am not sure of the exact situations; I assume it will not be null
though.

dupe of #1512

[advaith1]

documented that the guild embed is also known as the widget

semi-dupe of #1536 but inaccurate because it was renamed and referring to it as embed is deprecated

[ghost]

@advaith1 true, I didn't realise that until now. At the risk of sounding like I am being awkward, probably worth merging it here rather than removing it again and then having to fix the merge conflicts in the other issue, which seems to be inactive for the past week

[msciotti]

Looks good if you don't mind fixing the merge conflicts.

[ghost]

@msciotti fixed merge conflicts, cheers for pointing that out 👍