Clean up and fix Bundler-generated files

Minor cosmetic tweaks and other fixes:

  - killed an unnecessary comment
  - replaced some double quotes with singles
  - make use of `autoload` to get lazy-loading behavior and get rid of
    explicit requires
  - camel-case the class name; note the name of the gem itself remains
    as "pubsubhub" to avoid some unsightly underscores
  - set author, title, summary etc information in gemspec
  - remove Git-dependency from gemspec

Change-Id: I095ccb432d274fbd643330a90ef0bab3a18ebd2d
Reviewed-on: https://gerrit.causes.com/26271
Reviewed-by: Greg Hurrell <greg@causes.com>
Tested-by: Greg Hurrell <greg@causes.com>
Add dependency on Ruby 2.0.0

I'm about to import the PubSubHub files from the causes.git repo, and
they effectively depend on Ruby 2.0.0 because they use 2.0.0 syntax.

Make that dependency explicit in the gemspec.

Change-Id: I9fb4711004b402eb8e5e1150a28e0382a410daad
Reviewed-on: https://gerrit.causes.com/26272
Reviewed-by: Lann Martin <lann@causes.com>
Tested-by: Greg Hurrell <greg@causes.com>