Tags and a few descriptions

[burtlo]

Again went through and sprinkled some tags throughout the features and added a description or two where one was missing.

[dchelimsky]

We're using relishapp to display features as documentation, and there is no support for hiding tags like these, so I don't want to add them.

I do want the description you added for transactional examples, so I'll just merge that and close this pull.

If you have other descriptions you want to add or modify, please submit them as separate pull requests.

Thx!

[burtlo]

Thanks @dchelimsky