Make generator to parse data for performance improvement with large files

[manesioz]

Since some *.osm.pbf files are quite large, do you think it would be possible to yield each row of data instead of appending it to a dict? So that parse_osm_pbf() would become a generator. This would be great for my use-case, if you want I can start a PR for this feature if you think its useful/feasible. @mikeqfu