storage: fix formatting of container manual pages

The containers-storage(1) and many other manual pages were unreadable.
These files only have section headings (`##` in Markdown, `.SH` in roff)
and lack a title heading (`#`, `.TH`). Fix all of these instances with:

    sed -re '1s/^## (.+)/# \1/' storage/docs/containers-storage*.md -i

containers-storage.conf.5.md was somewhat readable, but was also fixed
up for consistency. Remove author info, already present in footer.
A similar problem in the common and image docs was ignored.

These manual pages still have some formatting issues, but this resolves
the main one. No idea whether this documentation is still up-to-date.

Fixes: #103
Signed-off-by: Peter Wu <[email protected]>

Author: Lekensteyn