Update platform diagram with Spring Cloud

The new umbrella project "Spring Cloud" is now part of the Spring
platform as an "IO Coordination" project.
Update links to new Pivotal website (pivotal.io)
Introduce support for asciidoctor inside tutorials

Due to plans regarding older tutorials, removed all markdown support. Also refactored asciidoctor utilities into common class and applied them to getting started guides as well.
Merge pull request #475 from gregturn/add-adoc-to-tutorials

Introduce support for asciidoctor inside tutorials
Upgrade to Spring Boot 1.1.8.RELEASE
Redirect deprecated guides URLs to /guides

Deprecated guides' URLs ("/guides/tutorials/rest,data,web") are now
retired and should redirect to "/guides" for the time being.
This change will be enhanced when Sagan will use Spring Framework 4.1.
Fix 98fbddfe3 with better URL rewriting

Use the embedded URLRewriterFilter instead of a regular controller.
Upgrade to Spring IO Platform 1.0.2

Upgrade to:
* Spring IO Platform 1.0.2
* Spring Boot 1.1.6.RELEASE
* upgrade various 3rd party dependencies
Clean gradle dependencies

* Clean dependency versions managed by Spring IO Platform
* Temporarily use a non-platform fixed version of Spring Framework