Fix PawSort (intro_sort and heap_sort)

Summary:
Implemented introspective sort :

• DPQS;
• pivots selected thanks to median-of-3 algo;
• quitting recursive sort through depth (apply heap-sort) or threshold (number of item in array < 17).

Based on http://www.cs.rpi.edu/~musser/gp/introsort.ps

Test Plan: Added tests for insertion_sort.

Reviewers: jcmcdonald

Reviewed By: jcmcdonald

Subscribers: jcmcdonald, jenkins

Tags: Announce [Control], BSS [Team], PawLIB [Project], Programming [Dept]

Differential Revision: https://phabricator.mousepawmedia.net/D240