Add deprecation notice and metadata

[kyzn]

It was noted that this module is deprecated at https://github.com/kablamo/VimDebug/issues/37#issuecomment-261698291

This patch adds a note that flags this module as deprecated, according to http://neilb.org/2015/01/17/deprecated-metadata.html

Please note that in order to make dzil build work on my environment, I had to do some more changes that is not included in this pull request: https://github.com/kyzn/VimDebug/commit/3d3607bfa12f15924cc8e99cbec644f9f14c0bce