a trie data structure

I implemented a simple trie data structure so as to be able to perform prefix searches on
objects that have a string as a key.

This is very useful if someone wants to implement an autocomplete feature.
(check this for a similar effort: http://pthurlow.github.io/triejs/)

This might be buggy and might also not conform with all the coding conventions.
If so, tell me to make the necessary changes.