Switch gem source to https://rubygems.org
Add Guardfile

The gemspec is not updated on purpose in order to not add a new dependency.
The presence of the Guardfile should do the right thing for environments with
guard installed, and should not harm otherwise.
Implement `default` (read-only)

This is the same as machine name except that default matches any
name. See `man netrc` for more details.
Merge pull request #17 from nerab/SupportDefaultHost

Implement `default` (read-only)