Support java directory

Add an example of two java files, Main.java and Another.java, where Main.java
depends on Another.java. This is part of a larger example of attempting to use
Nix to package these.

Also ignoring the *.class files that `javac <filename>` outputs.

.gitignore

@@ -4,3 +4,4 @@
 
 # Python
 __pycache__
+*.class

java/Another.java

@@ -0,0 +1,5 @@
+public class Another {
+  public static String whatis() {
+    return "Testing";
+  }
+}

java/Main.java

@@ -0,0 +1,6 @@
+public class Main {
+  public static void main(String[] args) {
+    System.out.println(System.getProperty("java.class.path"));
+    System.out.println(Another.whatis());
+  }
+}