[SPARK-2263][SQL] Support inserting MAP<K, V> to Hive tables

JIRA issue: [SPARK-2263](https://issues.apache.org/jira/browse/SPARK-2263)

Map objects were not converted to Hive types before inserting into Hive tables.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #1205 from liancheng/spark-2263 and squashes the following commits:

c7a4373 [Cheng Lian] Addressed @concretevitamin's comment
784940b [Cheng Lian] SARPK-2263: support inserting MAP<K, V> to Hive tables
[BUGFIX][SQL] Should match java.math.BigDecimal when wnrapping Hive output

The `BigDecimal` branch in `unwrap` matches to `scala.math.BigDecimal` rather than `java.math.BigDecimal`.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #1199 from liancheng/javaBigDecimal and squashes the following commits:

e9bb481 [Cheng Lian] Should match java.math.BigDecimal when wnrapping Hive output
SPARK-2038: rename "conf" parameters in the saveAsHadoop functions with source-compatibility

https://issues.apache.org/jira/browse/SPARK-2038

to differentiate with SparkConf object and at the same time keep the source level compatibility

Author: CodingCat <zhunansjtu@gmail.com>

Closes #1137 from CodingCat/SPARK-2038 and squashes the following commits:

11abeba [CodingCat] revise the comments
7ee5712 [CodingCat] to keep the source-compatibility
763975f [CodingCat] style fix
d91288d [CodingCat] rename "conf" parameters in the saveAsHadoop functions