Add maintainer

Wellcome yasuyk.
Tweak Package-Requires header
Tweak header
Remove Package-Version header

Version header of this package can be parsed by version-to-list, so
Package-Version is unnecessary.

For detais, See http://www.gnu.org/software/emacs/manual/html_node/elisp/Library-Headers.html.
Fix Code section comment
Remove helm-c-yas-version

Version header exists, so helm-c-yas-version is unnecessary.