implement Kendall's tau
add documentation, remove dependency on monad-primitive
fix indentation
add tests for Kendall, and fix one bug
add special cases test for Kendall
Remove some unfortunate uses of INLINE
Drop a ton more uses of INLINE

--HG--
extra : amend_source : c838454f332970db35c7bad687558e146ae6043e
Deduplicate definitions of square
Get rid of obsolete GHC clauses
Small fixlet of null check
Drop an unneeded import
Specialize the definition of sort
Split out Alexey's matrix code into its own module

--HG--
rename : Statistics/Test/KolmogorovSmirnov.hs => Statistics/Matrix.hs
Simplify some names
Upgrade to QuickCheck 2.7.5
Massively enrich the matrix support

We also add an ApproxEq type class, to try to keep testing a bit
saner.
Fix a compiler warning
Oops, missed some files
Add a transpose function
Fix some > 80-col lines :-(