version 0.9.27

 - Mailer: Fixed invalid Content-Type by @BlackPrincess
 - Mailer: Fixed #66 Fix hard code charset by @BlackPrincess
 - Mailer: Fixed #65 TODOs in RichMimeMessage
 - Enabled SKINNY_ENV environment variable
 - Renamed SkinnyEnv.Key to SkinnyEnv.PropertyKey