Really add everything related to BSON symbols.

I forget to commit everything I've wanted last time, so here's an amendment for
it. Also I didn't indicate I've updated the DefaultPredicate class (which I
did), sooo ... that's a wrap!

src/main/java/com/github/kohanyirobert/ebson/BsonObject.java

@@ -118,7 +118,8 @@ public enum BsonObject {
    * type.
    * </p>
    */
-  SYMBOL(BsonBytes.SYMBOL),
+  SYMBOL(BsonBytes.SYMBOL, DefaultPredicate.SYMBOL,
+      DefaultReader.SYMBOL, DefaultWriter.SYMBOL),
 
   /**
    * JavaScript code with scope.

src/main/java/com/github/kohanyirobert/ebson/DefaultPredicate.java

@@ -117,6 +117,16 @@ public boolean apply(Class<?> input) {
     }
   },
 
+  SYMBOL {
+
+    @Override
+    public boolean apply(Class<?> input) {
+      return input == null
+          ? false
+          : BsonSymbol.class.isAssignableFrom(input);
+    }
+  },
+
   INT32 {
 
     @Override

src/main/java/com/github/kohanyirobert/ebson/DefaultReader.java

@@ -180,6 +180,14 @@ private int optionToFlag(char option) {
     }
   },
 
+  SYMBOL {
+
+    @Override
+    Object checkedReadFrom(ByteBuffer buffer) {
+      return new BasicSymbol(buffer);
+    }
+  },
+
   INT32 {
 
     @Override

src/main/java/com/github/kohanyirobert/ebson/DefaultWriter.java

@@ -169,6 +169,15 @@ private boolean hasFlag(int flags, int flag) {
     }
   },
 
+  SYMBOL {
+
+    @Override
+    public void writeTo(ByteBuffer buffer, Object reference) {
+      ByteBuffer symbol = ((BsonSymbol) reference).symbol();
+      buffer.putInt(symbol.capacity() + 1).put(symbol).put(BsonBytes.EOO);
+    }
+  },
+
   INT32 {
 
     @Override

src/test/java/com/github/kohanyirobert/ebson/DefaultSymbolReaderWriterTest.java

@@ -0,0 +1,42 @@
+package com.github.kohanyirobert.ebson;
+
+import com.google.common.base.Charsets;
+import com.google.common.primitives.Ints;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+public final class DefaultSymbolReaderWriterTest extends AbstractReaderWriterTest {
+
+  private static final String SYMBOL_ALPHABET = "abcdefghijklmnopqrstuvwxyz";
+  private static final int MAX_SYMBOL_LENGTH = 1024;
+  private static final ThreadLocal<ByteBuffer> RANDOM_SYMBOL = new ThreadLocal<ByteBuffer>() {
+
+    @Override
+    protected ByteBuffer initialValue() {
+      StringBuilder sb = new StringBuilder();
+      for (int i = 0; i < BsonRandom.nextInt(MAX_SYMBOL_LENGTH); i++)
+        sb.append(SYMBOL_ALPHABET.charAt(BsonRandom.nextInt(SYMBOL_ALPHABET.length())));
+      ByteBuffer symbol = ByteBuffer.allocate(Ints.BYTES + sb.length() + 1)
+          .order(ByteOrder.LITTLE_ENDIAN)
+          .putInt(sb.length() + 1)
+          .put(sb.toString().getBytes(Charsets.UTF_8))
+          .put(BsonBytes.EOO);
+      symbol.flip();
+      return symbol;
+    }
+  };
+
+  public DefaultSymbolReaderWriterTest() {
+    super(DefaultReader.SYMBOL, DefaultWriter.SYMBOL);
+  }
+
+  @Test
+  public void randomSymbol() {
+    assertEquals(writeTo(new BasicSymbol(RANDOM_SYMBOL.get())), readFrom());
+  }
+}