SPARK-6454 [DOCS] Fix links to pyspark api

Author: Kamil Smuga <smugakamil@gmail.com>
Author: stderr <smugakamil@gmail.com>

Closes #5120 from kamilsmuga/master and squashes the following commits:

fee3281 [Kamil Smuga] more python api links fixed for docs
13240cb [Kamil Smuga] resolved merge conflicts with upstream/master
6649b3b [Kamil Smuga] fix broken docs links to Python API
92f03d7 [stderr] Fix links to pyspark api