dataframes.jl cleanup

Cleanup of the dataframe() function. Now, we write the response.data directly to the buffer (we don't need to chomp, to split or to write line-by-line to the buffer, and we don't need the `data` variable). I also changed variable names to better readability.

I just don't understand two things:

- Why don't we make use of multiple dispatch to make sure that the argument passed to our function is of the type `Response`? This lead us to the second question...
- Why don't we use names like `DataFrame()` and `TimeArray()` to our functions? They are, after all, just new constructors, with a `Response` object as argument