Add GemFire Support

Fixes GH PR #148 and PR #308 implementing a GemFire Adapter to support
clustered HttpSessions in Spring Session.

* Resolve SGF-373 - Implement a Spring Session Adapter for GemFire backing
a HttpSession similar to the Redis support.
* Add Spring Session annotation to enable GemFire support with
@EnableGemFireHttpSession.
* Add extesion of SpringHttpSessionConfiguration to configure GemFire using
GemFireHttpSessionConfiguration.
* Add implementation of SessionRepository to access clustered, replicated
HttpSession state in GemFire with GemFireOperationsSessionRepository.
* Utilize GemFire Data Serialization framework to both replicate
HttpSession state information as well as handle deltas.
* Utilize GemFire OQL query to lookup arbitrary Session attributes by name,
and in particular the user authenticated principal name.
* Implment unit and integration tests, and in particular, tests for both
peer-to-peer (p2p) and client/server topologies.
* Set initial Spring Data GemFire version to 1.7.2.RELEASE, which depends
on Pivotal GemFire 8.1.0.
* Add documentation, Javadoc and samples along with additional Integration
Tests.

Fixes gh-148

docs/build.gradle

@@ -16,6 +16,10 @@ liveReload {
 	docRoot asciidoctor.sourceDir.canonicalPath
 }
 
+repositories {
+	maven { url 'http://dist.gemstone.com/maven/release' }
+}
+
 asciidoctorj {
 
 }
@@ -25,6 +29,7 @@ tasks.findByPath("artifactoryPublish")?.enabled = false
 dependencies {
 		testCompile project(':spring-session'),
 				"org.springframework.data:spring-data-redis:$springDataRedisVersion",
+				"org.springframework.data:spring-data-gemfire:$springDataGemFireVersion",
 				"org.springframework:spring-websocket:${springVersion}",
 				"org.springframework:spring-messaging:${springVersion}",
 				"org.springframework.security:spring-security-web:${springSecurityVersion}",
@@ -61,4 +66,4 @@ asciidoctor {
 			'idseparator':'-',
 			'docinfo1':'true',
 			'revnumber' : project.version
-}
+}