allow look up of convertible types also in nested maps

[vandres]

This is a proposal to solve #47

[dalenguyen]

Hi @vandres, thanks for your contribution. I like the fact that you refactored a few helper functions. The nested key may not be a good practice because it applies to everything even though we may only one type of nested option (date or geo only).

I will merge this one and test it on a sample branch.