Tag list

When saving a Contact the new tags should be in the `tag_list` attribute, but when fetching a `tags_joined_by_comma` is returned. This makes is so that if you change `tags_joined_by_comma` it is submitted as `tag_list`, unless you are using `tag_list` directly (for compatibility). Should solve #8 

I also had to mess with the gemspec, to make the travis build pass, sorry.