Generate rust documentation on CI and publish to gh-pages automatically (#793)

Signed-off-by: Victor Porof <victor.porof@gmail.com>

.travis.yml

@@ -23,4 +23,12 @@ script:
     for manifest in $(find . -type f -name Cargo.toml); do
       cargo test --manifest-path $manifest --verbose --no-default-features --features sqlcipher
     done
+after_success:
+  - |
+    if [[ "$TRAVIS_PULL_REQUEST" = "false" && "$TRAVIS_BRANCH" == "master" ]]; then
+      cargo doc &&
+      echo "<meta http-equiv=refresh content=0;url=mentat/index.html>" > target/doc/index.html &&
+      git clone https://github.com/davisp/ghp-import.git &&
+      ./ghp-import/ghp_import.py -n -p -f -r https://"$GH_TOKEN"@github.com/"$TRAVIS_REPO_SLUG.git" target/doc
+    fi
 cache: cargo

README.md

@@ -8,6 +8,8 @@ The first version of Project Mentat, named Datomish, [was written in ClojureScri
 
 The Rust implementation gives us a smaller compiled output, better performance, more type safety, better tooling, and easier deployment into Firefox and mobile platforms.
 
+[Documentation](https://mozilla.github.io/mentat)
+
 ---
 
 ## Motivation