Expand completions to better support previews for more contexts

[erikkrieg]

Right now subcommands and options for some commands are not particularly well supported. There is a naive implementation of batman, but I don't have manual entries for many CLIs and there are many cases where subcommand names are passed into batman without the root command also being provided. This can sometimes match unrelated manuals and be misleading.

There are also many unsupported types for different apps and commands. So examples:

• kill listing processes
• git log listing commits