Added sort performance tests

Based on tests in https://github.com/kmsquire/SortPerf.jl, which are based on tests described in http://svn.python.org/projects/python/trunk/Objects/listsort.txt

Testing includes:
* all algorithms (QuickSort, MergeSort, InsertionSort, TimSort)
* range of sizes (2^6 -> 2^18)
* different datatypes (Int, Float, String)
* different data characteristics (random, sorted, reversed, 3 random exchanges, 10 random values appended, 4 unique values, all equal, quicksort median killer)

Also added a `timeit_init` macro, which allows some non-timed initialization to occur.