Create travis doc upload script

according to https://github.com/kmcallister/travis-doc-upload/blob/master/README.md

Author: phil-opp

.travis.yml

@@ -1,3 +1,5 @@
 language: rust
 rust:
   - nightly
+
+after_success: cargo doc && sh scripts/travis-doc-upload.sh

scripts/id_rsa.enc

@@ -0,0 +1,3 @@
+PROJECT_NAME=linked-list-allocator
+DOCS_REPO=phil-opp/linked-list-allocator.git
+SSH_KEY_TRAVIS_ID=5046af79ab8b

scripts/travis-doc-upload.cfg

@@ -0,0 +1,30 @@
+#!/bin/sh
+
+# License: CC0 1.0 Universal
+# https://creativecommons.org/publicdomain/zero/1.0/legalcode
+
+set -e
+
+. scripts/travis-doc-upload.cfg
+
+[ "$TRAVIS_BRANCH" = master ]
+
+[ "$TRAVIS_PULL_REQUEST" = false ]
+
+eval key=\$encrypted_${SSH_KEY_TRAVIS_ID}_key
+eval iv=\$encrypted_${SSH_KEY_TRAVIS_ID}_iv
+
+mkdir -p ~/.ssh
+openssl aes-256-cbc -K $key -iv $iv -in scripts/id_rsa.enc -out ~/.ssh/id_rsa -d
+chmod 600 ~/.ssh/id_rsa
+
+git clone --branch gh-pages git@github.com:$DOCS_REPO deploy_docs
+
+cd deploy_docs
+git config user.name "travis update bot"
+git config user.email "travis-update-bot@phil-opp.com"
+rm -rf *
+mv ../target/doc/* .
+git add -A .
+git commit -qm "update docs to $TRAVIS_COMMIT"
+git push -q origin gh-pages