One less iteration through layer values
One less iteration through layer values

Previously was iterating through a layer twice, once to get keys and values (tags/properties) and second time to iterate
through features (since features are placed before keys and values, however feature extraction require the property
pairs).

Now, it iterates through the layers, gathering all keys and values and putting the feature protobuf::message in a vector
to be iterated once all keys and values have been parsed.

karimnaaji/tangram-es,hjanetzek/tangram-es,tangrams/tangram-es,karimnaaji/tangram-es,cleeus/tangram-es,tangrams/tangram-es,tangrams/tangram-es,hjanetzek/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,xvilan/tangram-es,tangrams/tangram-es,xvilan/tangram-es,tangrams/tangram-es,tangrams/tangram-es,karimnaaji/tangram-es,hjanetzek/tangram-es,xvilan/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,xvilan/tangram-es,hjanetzek/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,cleeus/tangram-es,cleeus/tangram-es,karimnaaji/tangram-es