Replace email builder by a new implementation (#393)

* Update dependencies (#386)

* Update dependencies and set MSRV to 1.40

* update hyperx

* Use display instead of description for errors

* Make hostname an optional feature

* Envelope from headers

* Update hyperx to 1.0

* rename builder to message

* Cleanup and make Transport send Messages

* Update rustls from 0.16 to 0.17

* Move transports into a common folder

* Merge imports from same crate

* Add message creation example to the site

* Hide "extern crate" in doc examples

* Add References and In-Reply-To methods

* Add message-id header

* Add blog posts and improve doc examples

.github/workflows/test.yml

@@ -67,7 +67,6 @@ jobs:
       matrix:
         rust:
           - stable
-          - beta
     steps:
       - uses: actions/checkout@v1
       - uses: actions-rs/toolchain@v1

.github/workflows/website.yml

@@ -12,10 +12,10 @@ jobs:
     - uses: actions/checkout@master
     - run: cargo install mdbook --no-default-features --features output,search
     - run: cd website && mdbook build
-    - run: echo "lettre.at" > website/_book/html/CNAME
+    - run: echo "lettre.at" > website/book/html/CNAME
     - name: Deploy
       uses: peaceiris/actions-gh-pages@v2.5.1
       env:
         ACTIONS_DEPLOY_KEY: ${{ secrets.ACTIONS_DEPLOY_KEY }}
         PUBLISH_BRANCH: gh-pages
-        PUBLISH_DIR: ./website/_book/html
+        PUBLISH_DIR: ./website/book/html