Documentation: add description for repartitionAndSortWithinPartitions

Author: Madhu Siddalingaiah <madhu@madhu.com>

Closes #3390 from msiddalingaiah/master and squashes the following commits:

cbccbfe [Madhu Siddalingaiah] Documentation: replace <b> with <code> (again)
332f7a2 [Madhu Siddalingaiah] Documentation: replace <b> with <code>
cd2b05a [Madhu Siddalingaiah] Merge remote-tracking branch 'upstream/master'
0fc12d7 [Madhu Siddalingaiah] Documentation: add description for repartitionAndSortWithinPartitions