Move shell completion logic to Java

Refactor bash shell completion to move the majority of the logic into
the Java code. This commit also removes the need for the '--' prefix on
every command.

spring-boot-cli/src/test/java/org/springframework/boot/cli/command/OptionParsingCommandTests.java

@@ -22,6 +22,8 @@ import static org.hamcrest.Matchers.containsString;
 import static org.junit.Assert.assertThat;
 
 /**
+ * Tests for {@link OptionParsingCommand}.
+ * 
  * @author Dave Syer
  */
 public class OptionParsingCommandTests {