Move to into smtpapiheaders - which is where it has been living. Starts process of breaking this data up classily
Refactors smtpapi related methods into their own class. Deprecates poorly named setHeaders, addHeaders, etc that actually have historically been setting X-SMTPAPI headers only. Deprecated so that the library continues to work for those using addHeaders with that expectation
Missing unique_args
Version bump 1.1.1
Merge pull request #53 from sendgrid/sm-smtpapi-headers

Sm smtpapi headers