remove workaround for leveldb's broken setup.py

leveldb 0.193 doesn't depend on ez_setup being installed anymore.
fix bin_to_nibbles docstring
remove trie console_script

given the fact that it didn't work at all and the limited usefulness of
pyethereum.trie as a script, remove it.

those who like to run it anyway, may type "python -m pyethereum.trie
..." instead.
Merge pull request #52 from brainbot-com/small-cleanup

Small cleanup