Refactor SMS

Figured out how to simplify the Account logic! All packages will import the `act` package then anonymously embed the `Account` struct. The types that are embedding it inherit it's methods automagically.
Worked fine for sms & shortcodes so it should for everything else.

Also added `golint` and `go vet` to the travis build. Currently they're limited to sms & shortcodes because the linter will fail on every other package.

Changes to sms:
- got rid of unnecessary private methods. (involved ripping out some tests)
- tried a different style of keeping track of URL's, I think it keeps the namespace a bit cleaner
- standardized doing project imports prior to stdlib imports