#149 - Support for TTL and write time retrieval

Then I don't know how to do this correctly:

```scala
object NamedColumnRef {
  implicit class ColumnNameFunctions(val columnName: String) extends AnyVal {
    def writeTime: WriteTime = WriteTime(columnName)
    def ttl: TTL = TTL(columnName)
  }

  implicit def toNamedColumnRef(columnName: String): NamedColumnRef = ColumnName(columnName)
}
```

```
spark-cassandra-connector:root:wip-149> it:test
[info] Compiling 10 Scala sources to /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/target/scala-2.10/it-classes...
[error] /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/src/it/scala/com/datastax/spark/connector/rdd/CassandraRDDSpec.scala:440: value writeTime is not a member of String
[error]       .select("id", "value", "value".writeTime).collect().headOption
[error]                                      ^
[error] /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/src/it/scala/com/datastax/spark/connector/rdd/CassandraRDDSpec.scala:452: value ttl is not a member of String
[error]       .select("id", "value", "value".ttl).collect().headOption
[error]                                      ^
[error] /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/src/it/scala/com/datastax/spark/connector/rdd/CassandraRDDSpec.scala:468: value writeTime is not a member of String
[error]       .select("id", "value", "value".writeTime, "value".ttl).collect().headOption
[error]                                      ^
[error] /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/src/it/scala/com/datastax/spark/connector/rdd/CassandraRDDSpec.scala:484: value writeTime is not a member of String
[error]       .select("id", "value".writeTime, "value2".writeTime).collect().headOption
[error]                             ^
[error] /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/src/it/scala/com/datastax/spark/connector/rdd/CassandraRDDSpec.scala:496: value ttl is not a member of String
[error]       .select("id", "value".ttl, "value2".ttl).collect().headOption
[error]                             ^
[error] /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/src/it/scala/com/datastax/spark/connector/rdd/CassandraRDDSpec.scala:511: value writeTime is not a member of String
[error]  Note: implicit value mapper is not applicable here because it comes after the application point and it lacks an explicit result type
[error]     implicit val mapper = new DefaultColumnMapper[WriteTimeClass](Map("writeTimeOfValue" -> "value".writeTime.selectedAs))
[error]                                                                                                     ^
[error] /Users/jlewandowski/Projects/OpenSource/spark-cassandra-connector/spark-cassandra-connector/src/it/scala/com/datastax/spark/connector/rdd/CassandraRDDSpec.scala:524: value ttl is not a member of String
[error]  Note: implicit value mapper is not applicable here because it comes after the application point and it lacks an explicit result type
[error]     implicit val mapper = new DefaultColumnMapper[TTLClass](Map("ttlOfValue" -> "value".ttl.selectedAs))
[error]                                                                                         ^
[error] 7 errors found
[error] (spark-cassandra-connector/it:compile) Compilation failed
[error] Total time: 4 s, completed Dec 18, 2014 11:17:51 AM
```