Feature request: let Query.execute return a hash

[Benjamin Heitmann]

Currently Queries only return nested arrays with the results.

So if my query is:

results = Query.new.select(:p, :d).
      where(:p, RDF::type, SIOC::Post.class_uri).
      where(:p, DCTERMS::created, :d).
      where(:f, SIOC::container_of, :p).execute

Then if I want to iterate over the results I have to do it this way:

results.each do |r|
   # do something with r[0] and r[1]
end

If query.execute would return a hash using the symbols used for the query, then the whole thing
could be used in a much more readable way:

results = Query.new.select(:post, :date).
      where(:p, RDF::type, SIOC::Post.class_uri).
      where(:p, DCTERMS::created, :d).
      where(:f, SIOC::container_of, :p).execute

results.each do |r|
   # do something with r[:post] and r[:date]
end

This is especially usefull, when getting a lot of data from a single sparql query, in order to
optimize something for speed.

In order to not break backwards compatibility, this could be done only
if execute is called e.g. like this:

query.execute {:return => :hash }
or
query.execute( :hash )