Updated links in docs to reference html and pdf resources

resolves #730

Readded epubs to available doc types

spring-cloud-task-docs/src/main/asciidoc/index.adoc

@@ -10,7 +10,7 @@ Michael Minella, Glenn Renfro, Jay Bryant
 :spring-cloud-task-repo: snapshot
 :github-tag: master
 :spring-cloud-task-docs-version: current
-:spring-cloud-task-docs: https://docs.spring.io/spring-cloud-task/docs/{version}/reference
+:spring-cloud-task-docs: https://docs.spring.io/spring-cloud-task/docs/{spring-cloud-task-docs-version}/reference
 :spring-cloud-task-docs-current: https://docs.spring.io/spring-cloud-task/docs/current-SNAPSHOT/reference/html/
 :github-repo: spring-cloud/spring-cloud-task
 :github-raw: https://raw.github.com/{github-repo}/{github-tag}

spring-cloud-task-docs/src/main/asciidoc/preface.adoc

@@ -8,9 +8,9 @@ Think of it as a map for the rest of the document. You can read this reference g
 linear fashion or you can skip sections if something does not interest you.
 
 == About the documentation
-The Spring Cloud Task reference guide is available in {spring-cloud-task-docs}/html[html],
-{spring-cloud-task-docs}/pdf/spring-cloud-task-reference.pdf[pdf]
-and {spring-cloud-task-docs}/epub/spring-cloud-task-reference.epub[epub] formats. The
+The Spring Cloud Task reference guide is available in {spring-cloud-task-docs}[html] 
+and {spring-cloud-task-docs}/index.pdf[pdf],
+{spring-cloud-task-docs}/index.epub[epub] . The
 latest copy is available at {spring-cloud-task-docs-current}.
 
 Copies of this document may be made for your own use and for distribution to others,