added default to quandlsearch to be Codes that returns array of codes from search

This provides the following output while retaining the option to get the entire Dict

````julia
julia> quandlsearch("oil", results="4")
4-element Array{ASCIIString,1}:
 "EIA_TOTALOILSUPPLY_A_POLAND90"
 "LCA_NY_GDP_PETR_RT_ZS"
 "EIA_TOTALOILSUPPLY_A_UZBEKISTAN118"
 "EIA_TOTALOILSUPPLY_A_SLOVAKIA94"
````