select/search/generic queries

[KenjiTakahashi]

Hi,

As far as I can see, pydruid does not currently support "new" query types, i.e. "select" and "search". Will be nice to have them :-).

Maybe it would also make sense to expose the __post method, so we are able to send queries directly? Might also be useful if somebody wants to use pydruid as a "middleware", with queries prepared somewhere else.