Feature/distcache

Added distcache_gets()

## Usage

`distcache_gets(const string FILEPATH, object[] keys, const object defaultValue)::map<key_type, value_type>`

`distcache_gets(const string FILEPATH, object key, const object defaultValue)::value_type`

## Example
```
hive> desc lr_model;
> feature                 int
> weight                  float
```

```sql
-- Copy key/value table on HDFS to the distributed cache
add file hdfs://dm01:8020/user/hive/warehouse/kdd12track2.db/lr_model;

-- returns multiple values for each feature
create table test01 as
select 
  rowid, 
  distcache_gets('lr_model', features, cast(0 as float)) as weights
from 
  testing2;
```

```
hive> desc test01; 
> rowid                   bigint 
> weights                 map<int,float> 
```

```sql
-- returns single value for a feature
select 
  rowid, 
  distcache_gets('lr_model', features[0], cast(0 as float)) as weight
from 
  testing2
limit 100;
```