DATAMONGO-1720 - Add JMH based benchmarks for MappingMongoConverter.

Run the benchmark via the maven profile "benchmarks":

    mvn -P benchmarks clean test

Or run them customized:

    mvn -P benchmarks -DwarmupIterations=2 -DmeasurementIterations=5 -Dforks=1 clean test

Origin pull request: #483.

spring-data-mongodb-benchmarks/src/main/resources/logback.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+
+	<appender name="console" class="ch.qos.logback.core.ConsoleAppender">
+		<encoder>
+			<pattern>%d %5p %40.40c:%4L - %m%n</pattern>
+		</encoder>
+	</appender>
+
+	<root level="error">
+		<appender-ref ref="console" />
+	</root>
+
+</configuration>