Add Gemspec to Gemfile

Allows easier testing with bundler, makes making packages from repo easier too! :+1:
Adds output when no config file found

Helpful for figuring out what's missing
Set defaults for git user and provider to Github

These can then be changed when using another provider, such as:

```yaml
git_user: gitlab
git_provider_address: mycoolgitlabserver.foo.com
```
Remove endpoint constant
Adds output for which repo is being cloned from
Change to git pull method to use different users

Functionality for defaults means this won't make a difference unless you specify a user and provider address in the config, it'll default to `git@github.com`
Change pull to accept git_user and address
As a Gem, we should ignore Gemfile.lock

See: http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Merge pull request #29 from petems/allow_other_providers

Allow other providers