Remove trailing whitespace.
Implement `adjustWithKey`

Wrapper around `updateWithKey`.
Implement `adjust`.

Wrapper around `updateWithKey`.
Factored out naive update in tests.
Implemented `updateLookupWithKey`.

Now the base implementation of the update series.
Implemented `update`.
Rewrite test for foldl

The previous test ensured that foldr and foldl yield the same result.
This is only true for associative functions. The test now compares
against Data.Map's foldl.
implement mapEitherWithKey
Deleted trailing whitespace.
Implemented `split`.
Implemented `splitLookup`.
Use a combinator in place of a function

--HG--
extra : amend_source : 00481b425021a6356f51a8ca6ccfe3e17e9a23f6
Conditionally compile code requiring containers >= 0.5
Rewrite alter without using continuations.
Merge pull request #36 from isturdy/adjust

Implementations of adjust, adjustWithKey.
Simplify tests
Merge pull request #37 from archblob/alter_regression

Rewrite alter without using continuations.
Merge
Simplify t_mapEitherWithKey
minor change to mapEitherWithKey, replacing explicit \ with (***)