Upgrade documentation styling

Resolves gh-1640

Author: eleftherias

build.gradle

@@ -13,7 +13,7 @@ buildscript {
 	}
 
 	dependencies {
-		classpath 'io.spring.gradle:spring-build-conventions:0.0.28.RELEASE'
+		classpath 'io.spring.gradle:spring-build-conventions:0.0.32.RELEASE'
 		classpath "org.springframework.boot:spring-boot-gradle-plugin:$springBootVersion"
 	}
 }

spring-session-docs/spring-session-docs.gradle

@@ -25,6 +25,21 @@ dependencies {
 
 def versions = dependencyManagement.managedVersions
 
+asciidoctorPdf {
+    clearSources()
+    sources {
+        include "index.adoc"
+    }
+}
+
+asciidoctor {
+    clearSources()
+    sources {
+        include "index.adoc"
+        include "guides/*.adoc"
+    }
+}
+
 asciidoctorj {
 	def ghTag = snapshotBuild ? 'master' : project.version
 	def ghUrl = "https://github.com/spring-projects/spring-session/tree/$ghTag"