Train release 1.127.0

New features

* types: implement a serializable regex type (83d46ae)
* code: update to rust 2018 (e77ea7a)

Bug fixes

* scripts: ignore merge commits when generating changelog (489306b)
* errors: convert ses invalid domain error into a 400 (5926a06)
* db: remove unused DataType (d807e21)

Refactorings

* settings: implement Default in enum_boilerplate! (a9c9a1b)
* settings: promote LogFormat and LogLevel to enums (1ec10e9)

Other changes

* docs: minor readme editorialisation (8c8e29a)
* deps: update sendgrid (bf5486f)

* settings: rename `BounceLimit(s)` to `DeliveryProblemLimit(s)` (1d5…

…e817)

* settings: promote Env to an enum from a wrapped string (dba93f0)

* build: lower the debug level to decrease binary size (91a5173)
* package: create an automated release script (05acce1)