Updating the description and subject to use for internal commands wholesale.

Determine which internal commands are "externalish" and update the content with more detail. When fleshing out individual command to keep, will create separate ticket for each.
Determine which internal commands are just that and remove.

Old description:

The page that documents the splitVector command is not very informative: https://docs.mongodb.org/manual/reference/command/splitVector/#dbcmd.splitVector

I'd like to see the same information on this page as is on the other command pages, for example: https://docs.mongodb.org/manual/reference/command/split/#dbcmd.split:

• A couple sentences explaining what the command does.
• A table showing what fields the command takes, along with a description of each
• An example or two