Fix compilation issues (#60)

* Fix compiler and linter issues

* Fix compilation

* Serialize tests because of `swift-configuration`

Merge pull request #58 from fpseverino/update

Update package

Update README.md

Merge pull request #39 from MihaelIsaev/master

Fix `IncomingMessage` model and update to Vapor4 RC with Swift 5.2

Merge pull request #37 from MihaelIsaev/master

Upgrade to Vapor4

Merge pull request #35 from saicu/master

Multiple Domain Configuration

Merge pull request #34 from saicu/master

fix for sending without template data

Merge pull request #32 from saicu/master

Mailgun templates

Merge pull request #31 from madsodgaard/feature/eu-support

Add support for region selection

Merge pull request #29 from AAAstorga/master

Add inline support