Switch docs deployment from Travis CI to GitHub Actions (#563)

.github/actions/docs-prerequisites/action.yml

@@ -0,0 +1,7 @@
+name: 'Get Docs Prerequisites'
+description: 'Downloads all the necessary packages for building documentation'
+runs:
+  using: composite
+  steps:
+    - run: sudo apt-get install doxygen python3 python3-pip python3-setuptools  python3-sphinx 
+      shell: bash

.github/actions/generate-publish-doc/action.yml

@@ -0,0 +1,17 @@
+name: 'Generate Doc'
+description: 'Runs b2 on lib/gil/doc to generate documentation'
+inputs:
+  github_token:
+    description: 'Github Token for Access'
+    required: true
+runs:
+  using: composite
+  steps:
+    - run: |
+        echo "using doxygen ;" > ~/user-config.jam
+        cd ../boost-root/libs
+        ../b2 gil/doc
+        cd gil
+        chmod +x $GITHUB_WORKSPACE/.github/actions/generate-publish-doc/upload-script.sh
+        $GITHUB_WORKSPACE/.github/actions/generate-publish-doc/upload-script.sh ${{inputs.github_token}}
+      shell: bash

.github/actions/generate-publish-doc/upload-script.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+set -e # Exit with Non Zero exit Code
+
+# Save some useful information
+SHA=`git rev-parse --verify HEAD`
+
+mkdir temp-doc
+cd temp-doc
+git init
+
+git config user.name "Github Action Upload Docs"
+git config user.email "Github Action Upload Docs"
+
+git remote add upstream "https://$1@github.com/boostorg/gil.git"
+
+git fetch upstream
+git switch gh-pages
+
+
+if [ "${GITHUB_REF##*/}" = develop ]; then
+    rm -r develop
+    mkdir -p develop/doc
+    cp ../index.html develop/
+    cp ../doc/index.html develop/doc
+    cp -a ../doc/html develop/doc/
+else
+    rm index.html
+    rm -r html
+    cp ../doc/index.html .
+    cp -r ../doc/html .
+fi
+
+
+git add .
+
+# Commit the new version.   
+git commit -m "Deploy to GitHub Pages: ${SHA}"
+
+# Now that we're all set up, we can push.
+git push -q upstream HEAD:gh-pages

.github/actions/setup-boost/action.yml

@@ -0,0 +1,17 @@
+name: 'Setup-Boost'
+description: 'Downloads and sets up the necessary dependencies of Boost'
+runs:
+  using: composite
+  steps:
+    - run: |
+        REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+        BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+        cd ..
+        git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+        cd boost-root
+        cp -r $GITHUB_WORKSPACE/* libs/gil
+        git submodule update --init tools/boostdep
+        python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" gil
+        ./bootstrap.sh
+        ./b2 -d0 headers    
+      shell: bash

.github/workflows/docs.yaml

@@ -0,0 +1,17 @@
+name: Docs-Build
+on:
+  push:
+    branches:
+      - master
+      - develop
+
+jobs:
+  build-docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ./.github/actions/docs-prerequisites
+      - uses: ./.github/actions/setup-boost  
+      - uses: ./.github/actions/generate-publish-doc
+        with:
+          github_token: ${{ secrets.GIL_TEST_TOKEN }}