com.mongodb.hadoop.hive.BSONSerde.getValue: supporting quoted dots

I am using a legacy BSON: using dot characters for some keys.
But this library does not supports this, so I implemented 'quoted dot.'

I tested this feature in my aws ami 3.1.0 & spark 1.0.0 & shark 0.9.0.
My testing query for the shark is:

```sql
DROP TABLE test_external;

CREATE EXTERNAL TABLE test_external(
  my_data STRING
)
ROW FORMAT SERDE "com.mongodb.hadoop.hive.BSONSerDe"
WITH SERDEPROPERTIES('mongo.columns.mapping'='{"my_data":"my\\\\.data"}')
STORED AS INPUTFORMAT "com.mongodb.hadoop.mapred.BSONFileInputFormat"
OUTPUTFORMAT "com.mongodb.hadoop.hive.output.HiveBSONFileOutputFormat"
LOCATION '/data'
;

SELECT my_data FROM test_external ORDER BY my_data LIMIT 1;
```