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

(cherry picked from commit 2b233f5fc4beb2c6ed4bc142e923e96f8bad3ec4)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>