Update rails-erd.gemspec

Since rubyforge.org is no more, set the homepage of the project to the github repo
Merge pull request #77 from kerrizor/patch-1

Update rails-erd.gemspec
Basic travis.yml
Remove site directory as it's moved to branch gh-pages
Update readme with links to Github Pages instead of RubyForge
Merge pull request #80 from voormedia/migrate_site_to_gh_pages

Migrate site to Github Pages