* Smaller things:
** Fix the code to give fewer warnings when compiled with -Wall
There are tons of small things in the code that spit out warnings in GHC or
hlint. Fixing this would likely improve code quality a bit.
** Update this TODO
There is probably more things to do that aren't named in here.
* Larger things:
** Should we only allow bytestring as key to avoid serialize/deserialze?
This could give lower memory usage, since nodes could remains as packed
bytestrings at all times. Some c-functions could be introduced to manipulate
these in a safe yet efficient way (copy on change).
** Complete the implementations of findMin and findMax.
Currently, min and max values can only be located if they reside in an
outermost leaf. Due to the nature of eventual-balance and lazy rebalancing
this is not always the case. The outermost leaf could be empty.