Python API for KernelDensity
Author: MechCoder <manojkumarsivaraj334@gmail.com>
Closes#6387 from MechCoder/spark-7639 and squashes the following commits:
17abc62 [MechCoder] add tests
2de6540 [MechCoder] style tests
bf4acc0 [MechCoder] Added doctests
84359d5 [MechCoder] [SPARK-7639] Python API for KernelDensity