manpages: add separate pages for each command

This update includes separate pages for each command, as following the docker style, including sections on synopsis, description, an example, and list of options as needed.  These pages should be more useful to a user trying to find information on command usage.  In addition, this alphabetizes the usage error outputs for ostree and ostree admin to make it easier to find commands.

Some of these pages are more detailed than others, and could use a review for technical accuracy and/or any important omissions.