Allow actions to accept id and class attributes

[michaelrevans]

Fixes #44

Added

N/A

Changed

• pass @tag_attributes along to action, allowing for id and class attributes to be defined
• add spec for class and id in action
• update action documentation to reflect the changes

Notes

• The approach that I took now means that the class and id attributes have to be defined in what is commonly called action_config, although this config seems more aimed at the underlying action (the method, the path, success, failure, etc), so I'm not sure if adding the id and class here will make it seem cluttered or messy. Thoughts on this are welcome.
• I tried triggering the Circle build a few times after random failures by using amended commits (I can't trigger a build directly in Circle), but none of them passed, so I will probably need some assistance with that. The relevant specs all pass locally.