Add support for service tags

[mstine]

Interesting Go problem I just ran into...when I fork your repo, I end up changing the packaging. Seems like it will be a pain to merge these.

At any rate, this functionality works, so just pull the hunks that actually have functional impact.

[joefitzgerald]

Ahaa... when modifying an existing package, you should:

1. fork https://github.com/joefitzgerald/cfenv to https://github.com/mstine/cfenv
2. go get -u github.com/joefitzgerald/cfenv
3. cd $GOPATH/src/github.com/joefitzgerald/cfenv
4. git remote add fork https://github.com/mstine/cfenv.git
5. git checkout -b deserialization-of-service-tags
6. make your changes
7. git push fork deserialization-of-service-tags

[mstine]

OK..redoing this.