Adding serializer for BigDecimal.

based the implementation on what cassandra does.

core/src/main/java/me/prettyprint/cassandra/serializers/BigDecimalSerializer.java

@@ -0,0 +1,65 @@
+package me.prettyprint.cassandra.serializers;
+
+import static me.prettyprint.hector.api.ddl.ComparatorType.DECIMALTYPE;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+import java.nio.ByteBuffer;
+
+import me.prettyprint.hector.api.ddl.ComparatorType;
+
+/**
+ * Serializer implementation for BigDecimal
+ * 
+ * @author peter lin
+ */
+public final class BigDecimalSerializer extends AbstractSerializer<BigDecimal> {
+
+  private static final BigDecimalSerializer INSTANCE = new BigDecimalSerializer();
+
+  public static BigDecimalSerializer get() {
+    return INSTANCE;
+  }
+
+  @Override
+  public byte[] toBytes(BigDecimal obj) {
+	  return this.toByteArray(obj);
+  }
+
+  @Override
+  public BigDecimal fromByteBuffer(ByteBuffer byteBuffer) {
+    if (byteBuffer == null) {
+      return null;
+    }
+    int scale = byteBuffer.getInt();
+    byte[] bibytes = new byte[byteBuffer.remaining()];
+    byteBuffer.get(bibytes, 0, byteBuffer.remaining());
+    BigInteger bi = new BigInteger(bibytes);
+    // now we create an instance of BigDecimal with BigInteger and scale
+    BigDecimal value = new BigDecimal(bi, scale);
+    return value;
+  }
+
+  @Override
+  public ByteBuffer toByteBuffer(BigDecimal obj) {
+    if (obj == null) {
+      return null;
+    }
+    return ByteBuffer.wrap(toByteArray(obj));
+  }
+
+  public byte[] toByteArray(BigDecimal bigDecimal) {
+	  byte[] bigIntBytes = bigDecimal.unscaledValue().toByteArray();
+	  byte[] scaleBytes = IntegerSerializer.get().toBytes(bigDecimal.scale());
+	  byte[] bytes = new byte[scaleBytes.length + bigIntBytes.length];
+	  System.arraycopy(scaleBytes, 0, bytes, 0, scaleBytes.length);
+	  System.arraycopy(bigIntBytes, 0, bytes, scaleBytes.length, bigIntBytes.length);
+	  return bytes;
+  }
+
+  @Override
+  public ComparatorType getComparatorType() {
+    return DECIMALTYPE;
+  }
+
+}