Add sort implementation in Rust.
Use unsafe code in Rust sort function.

Change the Rust implementation of sort to use unsafe code in the tight
loops. This results in approximately C++ perf.
Fix conversion to nanoseconds
Merge branch 'master' of https://github.com/ahmedcharles/stepanov-conversations-course
code from the last three classes
code from today's lecture, plus cleanups
fix concept requirement
notes for lecture 5
rename iter.h -> iterator_adapter.h
code from last lecture, plus small fixes
tape: variable-sized contiguous container
re-enable is_sorted check
quicksort for linked lists
Merge remote-tracking branch 'upstream/master'