Revert "Revert "Support subdomain configuration""

This reverts commit f7fedfa25476befec4a36f16c26b8fb3b25c16dc.
Merge branch 'master' of github.com:recurly/recurly-client-ruby
Don't raise exception if subdomain isn't configured

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Always escape URI before appending [fix #92]

Signed-off-by: Stephen Celis <stephen@stephencelis.com>