Add data structures as a separate module (#3518)

* Remove data structures from core-java

* Add data-structures

* Update README with links to articles

* Add parent module reference

data-structures/.gitignore

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+/target/

data-structures/README.md

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+## Relevant articles:
+
+- [The Trie Data Structure in Java](http://www.baeldung.com/trie-java)
+- [Implementing a Binary Tree in Java](http://www.baeldung.com/java-binary-tree)

data-structures/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>com.baeldung</groupId>
+	<artifactId>data-structures</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+
+	<parent>
+		<groupId>com.baeldung</groupId>
+		<artifactId>parent-modules</artifactId>
+		<version>1.0.0-SNAPSHOT</version>
+	</parent>
+	<build>
+		<pluginManagement>
+			<plugins>
+				<plugin>
+					<groupId>org.codehaus.mojo</groupId>
+					<artifactId>exec-maven-plugin</artifactId>
+					<version>${exec-maven-plugin.version}</version>
+				</plugin>
+			</plugins>
+		</pluginManagement>
+	</build>
+</project>