always use bundle exec when running rake

- using bundle exec is necessary to use gem from source
upgrade to Asciidoctor 1.5.0.rc.4
Upgrade to Asciidoctor 1.5.0-rc.5
Resolve #44
Merge pull request #46 from anthonny/master

Resolve #44 - Add default stylesheet to dist
Fix CSS file and update to 1.5.0
Update bower.json to 1.5.0
Update package.json to 1.5.0
Change asciidoctor_default.css to asciidoctor.css
Last commit (67c5766) contain update to asciidoctor 1.5.0 in Gemfile
Update README.adoc

Add TravisCI image
Update bower.json

Ignore `dist/npm`
Update bower.json

Add asciidoctor-all in all format
update example and README for 1.5.0
Merge pull request #48 from mojavelinux/update-example-and-readme

update example and README for 1.5.0
Add docbook backend
Update README.adoc, bower.json ans package.json
Docbook isn't the main target of webapp, for this reason we choose to keep it separate
Merge pull request #49 from anthonny/docbook-backend

Docbook backend
Swith to shields.io and add npm version
Update README
Merge pull request #52 from Mogztter/issue-50

Add npm badges to README
Merge pull request #54 from Mogztter/readme

Update README
Merge master into integration-asciidoctor-master